CA2030867C - Write-on film surface and bags having a write-on stripe - Google Patents
Write-on film surface and bags having a write-on stripeInfo
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- CA2030867C CA2030867C CA 2030867 CA2030867A CA2030867C CA 2030867 C CA2030867 C CA 2030867C CA 2030867 CA2030867 CA 2030867 CA 2030867 A CA2030867 A CA 2030867A CA 2030867 C CA2030867 C CA 2030867C
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Abstract
The invention relates to a write-on surface derived by surface treatment (corona-discharge or other similar surface treatment) of a novel write-on composition. The write-on composition to be treated is characterized as a physical mixture of two substantially incompatible polymers and, optionally, a particulate material.
Description
- 20~867 WRITE-ON FILM SURFACE AND
BAGS HAVING A WRITE-ON STRIPE
FIELD OF THE INVENTION
The instant invention relates to writable or write-on plastic surfaces and to novel write-on compositions for use in providing a write-on surface on a bag body. In one embodiment the invention relates to a writable plastic film surface provided as a write-on area for a plastic bag whereby the user of the bag may conveniently write on the outer bag surface to provide easily viewable information concerning the contents or use of the bag.
BACKGROUND OF THE INVENTION
The prior art relating to the preparation of write-on plastic surfaces is replete with numerous examples of diverse methods of physically or chemically treating a plastic surface to improve the ability of the plastic surface to accept ink from a pen or, alternatively, a printing ink (collectively and generally referred to in the prior art and herein as "ink"). The ability of an ink to be retained or adhere to a surface is commonly referred to as the "wetting"
characteristic of the ink for that surface and reflects the extent of adhesion of the ink to the particular surface. This ability of the ink to wet the surface is also an indication of the writability of surface. Review of the prior art 203~67 relating to write on thermoplastic surfaces is set forth hereinafter.
The prior art has disclosed both chemical and physical treatment proceCcec for modification of the surface characteristics of thermoplastic materials.
For example, U.S. Patent No. 4,024,038 discloses chemical treatment of a plastic surface with a modification agent, e.g., a colvent, for the purpose of improving the adhesion characteristics of the surface of the plastic. Since chemical treatment is costly and difficult to implement in commercial manufacturing procesces, the most commonly employed means for modifying, i.e. "treating", a plastic surface to improve its adhesion characteristics is the use of corona-discharge treatment. The use of corona-discharge for treating the surface of a plastic to improve the ability of an ink to adhere to the plastic surface, i.e., to improve the adhesion characteristics of the film, is well established in the prior art, as represented by the disclosures of U.S. Patent Nos.: 2,810,933;
BAGS HAVING A WRITE-ON STRIPE
FIELD OF THE INVENTION
The instant invention relates to writable or write-on plastic surfaces and to novel write-on compositions for use in providing a write-on surface on a bag body. In one embodiment the invention relates to a writable plastic film surface provided as a write-on area for a plastic bag whereby the user of the bag may conveniently write on the outer bag surface to provide easily viewable information concerning the contents or use of the bag.
BACKGROUND OF THE INVENTION
The prior art relating to the preparation of write-on plastic surfaces is replete with numerous examples of diverse methods of physically or chemically treating a plastic surface to improve the ability of the plastic surface to accept ink from a pen or, alternatively, a printing ink (collectively and generally referred to in the prior art and herein as "ink"). The ability of an ink to be retained or adhere to a surface is commonly referred to as the "wetting"
characteristic of the ink for that surface and reflects the extent of adhesion of the ink to the particular surface. This ability of the ink to wet the surface is also an indication of the writability of surface. Review of the prior art 203~67 relating to write on thermoplastic surfaces is set forth hereinafter.
The prior art has disclosed both chemical and physical treatment proceCcec for modification of the surface characteristics of thermoplastic materials.
For example, U.S. Patent No. 4,024,038 discloses chemical treatment of a plastic surface with a modification agent, e.g., a colvent, for the purpose of improving the adhesion characteristics of the surface of the plastic. Since chemical treatment is costly and difficult to implement in commercial manufacturing procesces, the most commonly employed means for modifying, i.e. "treating", a plastic surface to improve its adhesion characteristics is the use of corona-discharge treatment. The use of corona-discharge for treating the surface of a plastic to improve the ability of an ink to adhere to the plastic surface, i.e., to improve the adhesion characteristics of the film, is well established in the prior art, as represented by the disclosures of U.S. Patent Nos.: 2,810,933;
2,844,731; 4,051,044; and 4,710,358. Use of corona-discharge treatment has typically addressed the treating conditions and not the compositional make-up of the plastic material being treated.
In addition to the patent literature, there is a significant body of non-patent, technical literature on corona-discharge treatment of plastic films. For example, the article "corona-discharge Treatment of Polyethylene Films I, Experimental Work and Physical Effects", Polymer engineering and Science, Vol. 18, No. 4 (March 1978) discusses the adhesion characteristics of corona-discharge treated polyethylene films and describes several testing procedures found useful in testing polyethylene films. Interestingly, the corona-discharge treated 2~30~67 films tested by the article's author were limited to unmodified polyethylene films (nbarefoot resins") and polyethylene films containing only low to medium concentrations of the slip additive commonly employed in the manufacture of polyethylene films.
The article reported some interesting results. The presence of 81 ip additive in the polyethylene film was noted to decrease the adhesion properties of the corona-discharge treated film, i.e., the treated film demonstrated reduced adhesion characteristics.
Significantly higher corona-Ai~chArge treatments were required to increase the surface adhesion properties. Further, the article reported that the addition of slip additives drastically changed both the polar characteristics and dispersion characteristics of the film's surface energy. The article noted that corona-discharge treatment of the slip additive (commonly referred to as "slip agents") associated with the polyethylene films did not result in an improvement in the "Wipe" test or "Adhesion" test employed in the article for evaluating the surface adhesion characteristics of the films. These tests are commonly employed to evaluate the writability/printability of a corona-discharge treated film surface as a function of the surface adhesive properties of the film surface (often referred to as the "wetting"
characteristics of the film surface by an ink).
Wetting characteristics of polyethylene films and the ability of such ~urfaces to have an ink adhere thereto have been di~cllc~e~ in the article entitled, "SURFACE CHARACTERIZATION OF CORONA
TREATED POLY~lnY~ENE FILMS", ANTEC 85, pages 269-272 (1985). This article examined the printability of polyethylene film and the effect of corona-discharge surface treatment on the polyethylene film surface 20~Q867 to improve ink wetting of the film surface, i.e., surface adhesion properties. The results reported by this article are interesting in many respects.
The author reported that, "Surface roughness is a barrier to wetting and yields higher than expected [contact~ angles" for unmodified low density polyethylene films (nbarefoot resins"), i.e. a polyethylene film not contAining slip or other processing additives. As expected, the author reported a clear relationship between the surface oxidation resulting from corona-discharge treatment and surface wetting of the evaluated barefoot polyethylene resins.
In another recent article entitled, "The Whole Story: Wettability, Corona Treaters and Compliance~
CO~v~ G MAGAZINE, September, (1986), the use of corona-discharge treaters is discussed in relation to in-line printing presses. The article is interesting in both its discussion of the effect of slip additives and use of water-based printing inks. The presence of slip additives on the surface of a modified film, i.e., slip additive-containing film, and the problems 81ip additives create in printing on the film surface are discussed. The author (Collins) reported interesting observations on the relationship of slip additives and the effect of corona-discharge treatment on slip additive-containing film. Several phenomena relating to the 61ip additives are discussed in the article, wherein Collins stated:
"It was observed that slip additives have a relatively low melt temperature. This means that subjecting the slip to excessive power levels would cause the slip additive to melt and become mobile, thereby obliterating the results of the treatment.
Corona treatment is strictly a surface phenomenon, he explained, with depth of 2~30867 penetration measured in angstroms. Whereas the surface slip additives can be El~ccescfully treated, subsequent movement through melting can cause the effect to be lost. Melt temperature of the slip, according to Pilla~
tests, appears to be in the neighborhood of 180- F."
After acknowledging the aforementioned phenomena the author ~i~c~c^e~ various alternatives to consider to resolve the problems encountered with slip additive-containing films. The thrust of the ensuing discussion related to adjustment of the corona-discharge treater and the role of the electrode and carrier roll in achieving optimum treatment results. (It is noted that the content of the article demonstrates that the author did not consider modification of the film composition as a means to improve the writability of the slip-additive-containing film.) Although the patent and non-patent literature contain numerous references to both chemical and physical treatments of a plastic surface for the purpose of improving the adhesion characteristics of a film, e.g. the adherence of an ink to the plastic surface, there has been relatively little prior art discussion on the importance of the chemical composition of the plastic material being treated.
Two patents discussing the composition of the plastic material as a means for affecting the adhesion characteristics of a plastic surface are disc~ e~ hereinafter.
An early reference to a plastic drawing material sheet is found in British Patent Specification No. 1,478,474. This British Patent discloses a plastic sheet material having a drawing layer which contains a crosslinked thermoplastic film-forming binder comprising more than 50% by 2030~67 weight of a polyvinyl butyral crosslinked by means of an etherified (polymethyl)-melamine in the presence of an acid catalyst, which polyvinyl butyral contained at least 18 per cent by weight of vinyl alcohol y~OU~3 before crosslinking. The British patent discloses the drawing layers as suitable for use with graphite pencils and ink. In addition, the drawing layers can contain ~toothing agents" selected from a wide range of particulate materials, including diatomaceous earth, glass powder, titanium dioxide, zinc oxide, kaolin and amorphous silica. The function of the "toothing agents" is somewhat unclear from the British patent, although the patentee states that a mixture of two toothing agents having different particle size and specific surface may be provided to improve the erasability of the drawing layer. One would assume that an improvement in erasability corresponds to a decrease in surface adhesion or a decrease in surface writability.
U.S. Patent No. 4,801,487 discloses an imprintable sheet of a plastic comprising a carrier sheet and a coating layer applied on at least one layer of the carrier sheet for receiving an imprint. The coating layer to be imprinted consists of a firm polymer matrix and microporous finely divided solid particles. The patentee describes the non-imprintable carrier sheet as a non-polar polymer such as polyethylene or polypropylene. The firm polymer matrix of the coating layer is disclosed at column 3, lines 30-39 as consisting substantially of several polymers. These polymers are contrasted by the patentee with the polyethylene and polypropylene polymers employed for forming the non-imprintable carrier sheet. For example, the firm polymer matrix (the coating layer to be imprinted) may be selected -2~3~8~i7 from a large class of polymers, including polyacrylates, polymethacrylates, polyesters, polystyrenes, poly-1-3-dienes, polyamides, polyurethanes, polyvinyl butyral, polyvinyl acetate alkyde resins, urea resins and resins modified with natural materials such as starch and casein. The "microporous finely divided solid particles" are disclosed as absorbent solid particles and are di~-c~s~e~ at column 3, lines 40-60. The extensive list of absorbent solid particles covers a wide range of solid materials having widely different chemical and physical properties, including white pigments and white or colorless fillers, such as aluminum oxide, barium sulfate, titanium dioxide, silicic acid, silicates, chalks, starch, melamine resins and/or formaldehyde resins. The function of the microporous finely divided solid particles cannot be surmised from this diverse random listing of materials. In fact, the patentee points out that the relevant criteria in selecting the microporous finely divided solid particles are that the particles be finely divided (having large specific surface area) and have a microporous internal structure. (See: column 3, lines 50-53) The specification and examples refer to the application of the firm polymer matrix as being a "coating"
applied on the non-imprintable carrier ~heet. The patentee actually refers to the firm polymer matrix coating as a "liguid primer". It is clear that the patentee's imprintable coating layer is related only to the firm polymer matrix with the microporous finely divided solid particles wherein the coating is applied as a liquid primer coating to a non-imprintable carrier sheet, e.g., a polyethylene or polypropylene film. The patentee discloses a corona-discharge treatment of the carrier sheet -before the primer liguid is applied. It is clear that the corona-discharge treated carrier sheet is not considered to be a write-on surface, (i.e., the coating provides this function) but is merely treated to improve adhesion of the liquid primer to the carrier sheet.
The addition of calcium carbonate additives for polyolefin films has been reported in the prior art. For example, the use of OMYACARB~
(OMYACARB CaC03 is sold by OMYA, 61 Main Street, Proctor, Vermont 05765) calcium carbonate mineral additive as a mineral additive in polyolefin films has been disclosed by the manufacturer to reduce the corona-discharge treatment levels by over 50 percent. Further, in sales literature on OMYACARB calcium carbonate mineral additive, it is noted that "Early studies also indicate that the decay of Corona Treatment over time is minimized by the inclusion of a calcium carbonate mineral additive. It is believed that the microroughening effect on the film surface that is imparted by these mineral additives allows the reduction in Corona level and the blockage of decay. It is important to note also that this micro-roughening effect enhances film printability. n The above discussion is instructive in demonstrating that the prior art to date has not appreciated the complexity of the problems associated with write-on plastic surfaces as such relate to compositional changes in the formulation of the plastic material. These problems (such problems not heretofore appreciated by the prior art) are further complicated when the user is attempting to write on a plastic film surface manufactured in conjunction with a commercial bag manufacturing process. It has been observed herein .
that additional problems arise in commercial bag manufacturing proces~Qs owing to the numerous and variable manufacturing parameters of these processes. For example, it is common practice to employ a number of chemical processing aids to assist in commercial manufacturing proceC~^A for bags and film products. Such additives are typically provided as a "masterbatch" to the plastic material being processed. For example, a common additive in the masterbatch is a slip additive (commonly called a "slip agent"). The slip agent is added to improve machine handling of the plastic material, e.g., a plastic film, by increasing the slipperiness of the surface of the plastic so as to facilitate its ease of passage through the manufacturing eguipment. The very slipperiness that is beneficial in the manufacture of the plastic material has been found to be detrimental to the end user's ability to write on the plastic film surface. The deterioration in the printability of the film as a result of film additives and/or oligomers is addressed in U.S. Patent No. 4,832,772 wherein a physical surface "wiping" step in employed and is preferably employed with a preparatory solvent treatment of the surface. U.S. Patent No.
4,832,772 discloses a process for wiping off a weak lay on the film surface containing oligomers and additives, although, surprisingly, no discussion of the nature of the "additives" is provided by the patentee.
As aforementioned, the use of a corona-discharge treatment of a plastic surface has been generally found to improve the writability or printability of slip agent-cont~in;ng plastic materials by oxidizing the film surface and, if slip agent is present, "burning-off" a portion of the ..~
slip aqent on the film surface. A discussion of the effect of corona~ chArge treatment is set forth in the recent article by James F. Carley and P. Thomas Kitze, entitled, "Corona-DiE^h~rge Treatment of Polyethylene Films. I. Experimental Work and Physical Effects", POLYMER ENGT~ T~G AND SCIENCE, Vol. 18, No. 4 (March, 1978). The article is instructive in its disclosure that no changes in surface topography as a result of commercial corona-discharges are believed to contribute to practical adhesion phenomena and, further, that very high corona-di~ch~rge treatment was required to affect slip additives at the surface of polyethylene It has been found herein in accordance with the instant invention that this "burning off" effect and the associated improvement in surface adhesion characteristics is a short-lived surface effect when slip agent is present in the plastic composition or in close proximity to the plastic composition. This observation stems from the fact that corona-discharge is a surface treatment. The slip agent present in the bulk plastic composition is not affected by the corona-discharge treatment. It has been observed that this "bulk" ~lip agent in the plastic composition migrates to the corona-discharge treated surface as time passes, i.e., as the film ages, and the amount of slip agent at the surface increases with time. Thi~ naging phenomenon" is related to the time the film has aged as well as the ambient conditions, e.g., temperature, under which the film has aged. Further, during many manufacturing proces~^~, e.g., during the manufacturing of plastic bags and plastic films, the plastic bags and plastic films are stacked or placed on a roll in such a manner that film ~urface treated by corona-discharge contacts an untreated film 2030~67 ..
surface having a greater amount of slip agent on the film surface that i6 present on the corona-discharge treated film surface. Once again, the net result of this contacting is an increase in amount of slip agent on the corona-~i~chArge treated film surface as a result of the physical contacting of the two film ~urfaces.
The prior art has not appreciated and, accordingly, has not addressed the aforementioned problems associated with write-on plastic surfaces.
Further, the unique problems associated with write-on surfaces associated with plastic bags has not been appreciated as to the unique problems associated with bag surfaces in physical contact with slip agents. As a result of this lack of appreciation, the prior art has not proposed effective means by which the write-on characteristics of plastic surfaces may be improved other than by simple mechanical or chemical surface treatment which are not effective for plastic surfaces that have undergone aging in the presence of slip agents.
The instant invention addresses these problems by providing a write-on composition suitable for corona-discharge (or other surface treatment providing a similar surface treating effect) having improved resistance to 61ip agent interference with the writability of the write-on film ~urface.
Further, the instant invention addresses the unique problems associated with the commercial manufacture of plastic bags having a bag body formed from a plastic film containing at least one slip agent component and having at least one write-on surface on at least one wall of the bag body.
D-lSS84 ~ 2~3~867 SUMMARY OF THE lNv~NllON
The instant invention relates to a writable plastic surface (preferably a plastic film surface) formed by corona-~isrhArge treatment (or other similar surface modification treatment) of a novel write-on composition. The write-on composition to be treated is characterized as comprising: a) a physical mixture of two polymers, as described in detail hereinafter; and, optionally, but preferably, b) particulate material present in an effective amount to further improve the writability of the corona-discharge treated plastic surface.
In one embodiment the write-on surface comprises a corona-Ai~c~rge treated write-on film composition wherein the write-on film composition, preferably sans slip agent, is coextruded with a bag film containing a slip agent, preferably a polyethylene film. A particulate material may be present in an effective amount in the write-on composition to aid in a reduction in the detrimental effect of slip agent on the writability of the corona-discharge treated writable film surface. The write-on film surface may also be beneficially provided with an embossed pattern.
In a further embodiment the write-on composition to be corona-discharge or surface treated is formed as a film which i8 substantially sans slip agent, i.e., formed substantially in the absence of slip agent or contains no slip agent additive. In this embodiment the write-on composition may be associated with a bag body and formed as a layer in a co-extruded ~lip agent-containing bag film.
In a further embodiment the write-on composition comprises a ma~or amount of polyolefin resin, e.g., polypropylene, high density polyethylene and/or low density polyethylene, as the first polymer and a minor amount of a polyisobutylene polymer as the second polymer, as hereinafter ~;c~ ced.
In a further embodiment the invention relates to a bag having a write-on surface and to a stack of bags with a write-on surface.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a 200 X photomic~o~aph illustrating a film surface not of the instant invention showing a non-wetting surface when the film surface is not corona-discharge treated.
FIG. 2 is a 2000 X photomic~o~aph illustrating a portion of the film of FIG. 1.
FIG. 3 is a 200 X photomi~Loy~aph illustrating a portion of a film the same as shown in FIG. 1 but corona-discharge treated at 63.8 watts per square inch.
FIG. 4 is a 2000 X photomi~oyLaph illustrating a portion of the film of FIG. 3.
FIG. 5 is a 200 X photomic~oy~aph illustrating a film surface containing a non-wetting surface having an embossed surface, no slip agent and which has not been corona-discharge treated.
FIG. 6 is a 2000 X photomi~Gyraph illustrating a portion of the film of FIG. 5.
FIG. 7 is a 200 X photomi~o~aph illustrating a film surface of a write-on film (containing a polyisobutylene component according to the instant invention) before corona-discharge treatment.
FIG. 8 is a 2000 X photomic~oy~aph illustrating a portion of the film of FIG. 7.
FIG. 9 is a 200 X photomic~o~Laph illustrating the same film surface depicted in FIG. 7, except the surface has been corona-di~chAFge treated at 63.8 2~asG7 watts per square inch.
FIG. 10 is a 2000 X photomicrograph illustrating a portion of the film of FIG. 9.
FIG. 11 is a 200 X photomic.oyLaph illustrating a film cont~ini~g 3000 ppm 61ip agent and a TiO2-containing white masterbatch with 10 weight percent of a SYLOID~ particulate ~ilica which has not been corona-~i~ch~rge treated.
FIG. 12 is a 2000 X photomic~GyLaph illustrating a portion of the film surface depicted in FIG. 11.
FIG. 13 is a 200 X photomic~oyLaph of the film shown in FIG. 11 which has been corona-discharge treated at 44.6 watts per square inch (watts/in2).
FIG. 14 is a 2000 X photomi~LG~Laph illustrating a portion of the corona-~i~ch~rge treated film surface depicted in FIG. 13.
FIG. 15 is a 2000 X photomic.o~aph illustrating a portion of the film surface depicted in FIG. 16.
FIG. 16 is a 200 X photomic~oyLaph illustrating a film containing and a TiO2-containing white masterbatch with 10 weight percent SYLOID~
particulate silica and which was corona-discharge treated at 46.6 watts per square inch.
FIG. 17 is a 200 X photomi~Lo~Laph illustrating a film surface of a write-on film containing a polyisobutylene component, 1000 ppm 61ip agent, 5000 ppm Super Floss~, and 4.5 wt. % of a white masterbatch, and which was corona-discharge treated at 44.6 watts per square inch.
FIG. 18 i6 a 2000 X photomic~cy.aph illustrating a portion of the film ~urface depicted in FIG. 17.
FIG. 19 i6 a 200 X photomicLoyLaph illustrating a film surface of a write-on film containing a 2030~7 polyisobutylene component (~Xx~T~R~ PA-30) with 10 weight percent SYLOID~ particulate silica and which was corona-~i~chArge treated at 44.6 watts per square inch.
FIG. 20 is a 2000 X photomi~Gy.aph illustrating a portion of the film ~urface of FIG.
19 .
FIG. 21 i8 a 200 X photomicLGyLaph illustrating a film surface of an aged write-on film according to the invention containing a polyisobutylene component, a SYLOID~ particulate silica and which was not corona-discharge treated.
FIG. 22 is a 2000 X photomic}o~aph illustrating a portion of the film surface depicted in FIG. 21.
FIG. 23 is a 200 X photomic~o~Laph illustrating a film similar to that shown in FIG. 21 except that ~Xx~T~R~ PA-30 was replaced with ~Xx~roR~ PA-50.
FIG. 24 is a 2000 X photomi~L~yLaph illustrating a portion of the film surface depicted in FIG. 23.
FIG. 25 is a 200 X photomic~.aph illustrating the film depicted in FIG. 21 after being aged at 140 degrees F for 28 days.
FIG. 26 is a 2000 X photomicLG~Laph illustrating a portion of the aged film of FIG. 25.
FIG. 27 is a 200 X photomic~yLaph illustrating the film depicted in FIG. 23 after being aged at 140 degrees F for 28 days.
FIG. 28 is a 2000 X photomi~L~yLaph illustrating a portion of the film surface depicted in FIG. 27.
FIG. 29 is a 200 X photomic~y~aph illustrating a portion of a low density polyethylene film surface containing a 10 wt. % of polyisobutylene component and 5 wt. % calcium carbonate component.
FIG. 30 is a 2000 X photomi~LGy.aph illustrating a portion of the film ~urface of FIG. 29.
FIG. 31 is a 200 X photomi~Gy~aph illustrating a portion of the film surface of a film similar to that shown in FIG. 29, except 20 wt. % of the polyisobutylene component was employed.
FIG. 32 is a 2000 X photomi~o~Laph illustrating a portion of the film surface of FIG. 31.
FIG. 33 is a 200 X photomiclG~Laph illustrating a portion of the film surface similar to that shown in FIG. 29, except 10 wt. % calcium carbonate was employed.
FIG. 34 is a 2000 X photomic~oyraph illustrating a portion of the film surface of FIG. 33.
FIG. 35 is a 200 X photomic,oy~aph illustrating a portion of the film surface similar to that shown in FIG. 29, except 20 wt. % of a polyisobutylene component was employed and 20 wt. % calcium carbonate was employed.
FIG. 36 is a 2000 X photomic~G~aph illustrating a portion of the film surface of FIG. 35.
FIG. 37 is a perspective view of a flexible container including a write-on surface in accordance with the invention and an optional reclosable fastening device.
FIG. 38 is a perspective view of the sidewall of a flexible container showing a write-on stripe coextruded with a bag film.
DETAILED DESCRIPTION OF THE 1NV~N1~1ON
In its broadest sense the invention relates to a writable plastic surface suitable for use as a write-on or an imprintable surface. The ability of a plastic surface to accept an ink, e.g., from an ink pen or an ink printing process, is generally referred to herein as the "writability" or the "write-on" characteristic of the plastic surface and reference to a "write-on" surface herein includes the application of ink to a surface by use of a ballpoint pen, a printing process or other means known in the prior art. The instant invention relates to a writable plastic surface derived by corona-discharge treatment (or other similar physical or chemical surface treatment) of a write-on composition. The write-on composition to be treated is generally characterized as: a) a physical mixture of two substantially incompatible polymers; and, optionally, b) a particulate material present in an effective amount to improve the writability of the corona-discharge treated film surface. The use of so called "corona-discharge treaters" to treat plastic surfaces is well known, as evidenced by articles such as "The whole story: wettability, corona treaters and compliance", CONVERTING MAGAZINE, September 1986.
In one embodiment the write-on composition may contain a slip agent and is formed into a film but is preferably sans slip agent. The film surface is corona-discharge treated to provide a write-on film surface having improved writability upon aging.
In a further embodiment a write-on film is coextruded with a polyolefin film, e.g., a polyethylene film, containing a slip agent and the write-on composition is provided as a write-on surface sans slip agent. Further, a particulate material may be present in an effective amount to interfere with the negative affect that migrating slip agent has on the writable film surface as the film ages. As discussed hereinafter the presence of slip agent in the polyolefin bag material and write-on stripe portion of a bag decreases the writability of the write-on surface, especially as the film undergoes aging after its manufacture. In a further embodiment the write-on ~urface is a film comprising a major amount of a mixture of low density polyethylene and high density polyethylene as a first polymer and a minor amount of a polyisobutylene as the second polymer, preferably provided as a polyisobutyler.e ~GI.~aining material such as ~x~ToR~ PA-30 or ~xx~T~R~ PA-S0, as hereinafter discl~cse~.
The invention also relates to a bag having a write-on surface, a stacked bag article comprising a plurality of bags having a write-on surface, e.g., a write-on stripe.
Although corona-discharge treatment has generally been found to be useful in improving the write-on characteristics of a plastic surface, including plastic film surfaces, it has been observed herein that corona-discharge treatment alone is not suf-ficient to provide an acceptable write-on surface for many end use applications.
This writability problem becomes especially acute when the write-on surface of interest is provided on a bag body formed from a thermoplastic film formed with a slip additive. The presence of the slip agent has been observed to be an especially acute problem as the film ages, since slip agent has been observed to bleed to the film 6urface. Further, the rate of bleeding of the slip agent to the film surface has been observed to increase with increasing temperature. The write-on characteristics of a write-on area are even further complicated when the write-on area is provided as a write-on area manufactured in conjunction with heretofore commercially employed bag manufacturing proc~Cces. The unique problems associated with write-on surfaces and bag manufacturing will be discussed hereinafter in conjunction with one embodiment of the instant invention.
The write-on composition of the instant invention is generally characterized as comprising two polymers wherein the second polymer is substantially incompatible in the first polymer.
The term "substantially incompatible" is used herein to denote a polymer mixture wherein at least one polymer component forms identifiable particles in the polymer mixture when the polymer mixture is extruded as a film composition. In one embodiment of tbe instant invention the write-on composition comprises a major amount of a low density polyethylene and a minor amount of a polyisobutylene-containing polymer blend. Two such polymer blends found to be useful in the instant invention are sold by Exxon Chemical Company, P.O.
Box 3272, Houston, Texas, 77253-3272, under the product trade designations ~xx~TOR~ PA-30 and ~X~TOR~ PA-50. ~X~TOR~ PA-30 is a pelletized polyisobutylene alloy and modifier comprising a blend of polyisobutylene and polypropylene in a weight ratio of about 1 to 2, respectively. Typical properties of T~XX~TOR~ PA-30 are as follows:
EXXELOR~ PA-30 Property Value ASTM Method Melt Index(l90-C), g/lOmin 0.15 D1238(Condition E) Melt Flow Rate (230-C),g/lOmin 0.50 D1238(Condition L) Density,g/cc 0.91 D1505 Vicat Softening Point(200g),-F 310 D1525 Hardness (5sec, Shore A) 85 D2240 Flexural Modulus, psi 6,150 D790 ~xx~ToR~ PA-50 is a pelletized elastomeric concentrate comprising a blend of a polyisobutylene and a high density polyethylene in a weight ratio of about 1 to 2, respectively. Typical properties ~XX~T~R PA-50 are as follows:
~X~T~R~ PA-50 ProDerty Value ASTM Method Melt Index(l90-C), g/lOmin 0.23 D1238(Condition E) Melt Flow Rate (230-C),g/lOmin 0.65 D1238(Condition L) Density,g/cc 0.924 D1505 Vicat Softening Point(200g),-F 253 D1525 Hardness (5sec,Shore A) 78 D2240 Flexural Modulus, psi 6000 D790 The first polymer of the write-on composition is typically a polyolefin, e.g., polyethylene, polymer (including ultra-low density, low density, medium density and high density) owing to their low cost but may be other polymeric materials heretofore known in the art. The first polymer may be selected from a wide range of polymers including polyethylenes, polypropylene, polybutylenes, butadiene/styrene, polyvinyl alcohol and the like.
Further, the first polymer may comprise a homogeneous blend of one or more polyethylene polymers and one or more other polymers, e.g., it has been observed that a first polymer comprising a mixture of low density polyethylene and a polyvinyl alcohol or a butadiene/styrene polymer may be useful as the first polymer in the two polymer mixture of the write-on composition. The use of a polyvinyl alcohol or butadiene/styrene as a component in a mixture with polyethylene is believed to sequester the migration of 61ip agent, although the mechAnism of the interaction of the 61 ip agent and the polyvinyl alcohol or butadiene/styrene is not understood at present.
The second polymer is preferably a polyisobutylene polymer (including physical mixtures of polyisobutylene with polypropylene, the various polyethylenes and the like) when the first polymer is a polyolefin, although other substantially incompatable polymers may be employed. As aforementioned, the operative parameter is selecting the first and ~ec~nA polymers is the substantial incompatibility of the -~conA polymer in the first polymer, as herein described.
The write-on composition may also contain a particulate material to improve write-on characteristics, especially when the write-on film undergoes aging. The particulate material is present in an effective amount to reduce interference of the slip agent at the write-on surface as compared to the writability that would be observed if the particulate material were not present in an effective amount. The role of the particulate material in the improvement of the writability of the write-on surface is believed to result from several factors. Although not wishing to be bound by any theory, it is believed that when properly selected the particulate material will provide two distinct functions. First, the particulate material may interact with the slip agent to inhibit its migration i.e., bleeding, to the write-on surface. Second, the particulate material may act as a ro~g~ing agent for the write-on surface. This roughening effect may provide several advantages peculiar to the adherence of ink to the surface by use of an ink pen as opposed to printing on the ~urface. Since the slip agent may collect in small pits formed by several particles of the particulate material, the slip agent may be below the ~urface of the write-on surface over which the ink is contacted and, accordingly, does not interfere with the writability of the write-on surface. Further, the "roughness"
--- 2~30867 characteristic of the particulate material is also believed to be beneficial when the write-on surface is written upon with a ballpoint pen, since the roughness of the surface is believed to beneficially aid in the mechAn~cal rolling of the ballpoint pen as it moves across the write-on 6urface. Further, the use of a particulate solid, such as calcium carbonate, may act as a cleaning aqent for the ball point of the pen to assigt in dislodging 61ip agent picked up by the pen during writing. It has been observed that not all particulate materials are useful, since use of talc was not observed to p~ovide a beneficial improvement in the writability of the write-on surface.
The selection of the first polymer and second polymer is related to the substantial incompatibility of the second polymer in the first polymer. The first polymer and cecon~ polymer are selected such that identifiable particles of the second polymer are present in the first polymer.
FIGS. 1 to 36 in the instant application demonstrate the identification of the second polymer particles by use of an electron sc~nning microscope. Although the relative amount of the first polymer and the second polymer will be related to the aforementioned substantial incompatibility, the first polymer will typically be present in a major amount (i.e., over fifty percent (50%) by weight) of the write-on composition. The secon~ polymer will typically be present in a minor amount (i.e., less than fifty percent (50%) by weight) of the total write-on composition.
It has been found that when the first polymer is a low density polyethylene having a density between about 0.915 to 0.940 (of the type commonly employed in the manufacture of thermoplastic bags and film) and/or polypropylene and the second polymer is a polyisobutylene-containing material such as ~Xx~T~R~ PA-30 or ~xxFT~R~ PA-50, that the aforementioned "substantially incompatible"
criteria are met. In one embodiment a low density polyethylene (formed with a l-butene, l-hexene or l-octene comonomer) having a density of between about 0.915 and about 0.940 g/cm3, preferably between about 0.915 and about 0.930 g/cm3 (typically having a melt index of between about 0.6 to 1.2) is employed at between about 50 wt. % and about 95 wt. % of the write-on film composition and a polyisobutylene/polypropylene mixture (sold under the Trademark ~xx~T~oR~ PA-30 by EXXON Chemicals Company) or a polyisobutylene/high density polyethylene mixture (sold under the trademark ~xx~ToR~ PA-50 by Exxon Chemicals Company) comprises between about 5 and about 20 weight percent of the write-on composition. The aforementioned discussions on the substantial incompatibility of the second polymer in the first polymer do not include any other polymer present in a polymer blend, unless such polymer(s) also meets the aforementioned criteria of substantial incompatibility, i.e., the first polymer and/or second polymer may themselves each comprise more than one polymer component. With respect to the use of ~xx~T~R~ PA-30 and ~xx~T~R~ PA-50 as the second polymer component it has been observed that the polypropylene and the high dénsity polyethylene present as carrier polymers for the polyisobutylene polymer in the ~xx~T4R~ PA-30 and ~Xx~TnR~
PA-50, respectively, do not meet the compatibility requirements for a second polymer when the first polymer i6 selected to be a low density polyethylene and, therefore, such carrier polymers should be 20~0867 treated as first polymer components in determining the relative weight percents of the first polymer and second polymer.
In one embodiment a polyisobutylene-containing material is employed as a component of the write-on composition (~X~T~R~ PA-50) and is present as a minor amount of the write-on composition with the major component comprising a low density polyethylene. Since ~xx~r~R~ PA-50 (and ~Xx~oR~
PA-30) is a polymer mixture (containing about 67 weight percent polyisobutylene and 33 weight percent of a high density polyethylene), the overall weight percent of polyisobutylene polymer in the write-on composition will generally be between about 3.25 weight percent and about 13.0 weight percent polyisobutylene, based upon the total weight of the polymeric components (e.g., polyisobutylene, low density polyethylene and high density polyethylene) in the write-on composition. In general the preferred low density polyethylene material employed as the major component with the aforementioned minor component (polyisobutylene-containing material) is characterized as having a density between about 0.915 and about 0.940 g/cm3, preferably between about 0.915 and about 0.930 g/cm3, and also typically characterized by a melt index of between about 0.6 and about 1.2. Further, when the write-on composition is one layer of a two-layer coextruded film structure, wherein the other layer is a slip agent-containing low density polyethylene bag film (routinely containing between about 500 ppm and about 2500 ppm elip agent, e.g., a C18 to C22 fatty acid amide, ~uch as ecuramide), it has been observed that it is preferred to have the write-on film comprise greater than about 30 percent of the combined total thickness of the write-on film and bag - 2030~67 film, preferably greater than 50 percent of the combined thickness. It has been observed that by making the thick~esR of the write-on film layer greater than about 30 percent of the total multilayer film thickness that the amount of slip agent which will bleed from the underlying slip agent-containing bag film to the write-on film ~urface is beneficially controlled, whereby the writability of the write-on surface is improved. Reference i~ made to FIG. 38 wherein a perspective view of such a multilayer, coextruded film is shown.
As aforementioned, the write-on composition may alæo contain a particulate material to improve the writability of the composition, when the write-on composition contains or is adjacent a material containing a slip agent. It has been observed that by providing an effective amount of a particulate material, i.e., an amount effective in reducing the detrimental effect of slip agent on writability of the surface of an article or film formed from the write-on composition, that the writability of the write-on surface as it ages is improved, as compared to the writability on the surface if the particulate material is not employed in an effective amount.
Although, the selection of the particulate material and its relationship to the first polymer and second polymer is not fully understood, the selection is believed to be related to the ability of the selected particulate material to chemically and/or physically interact with a selected slip agent whereby the detrimental effects of slip agent on surface writability is decreased as a result of the addition of the particulate material to the write-on film composition.
One or more slip agents, e.g., preferably one or more C18 to C22 fatty acid amides, may be used in 2030~67 the bag film and the write-on composition, although it is preferred that no slip agent be employed in the write-on composition i.e., the write-on composition is preferably sans 81ip agent. This reference to "sans slip agent" refers to the write-on composition as formed, e.g., as extruded, and not to the write-on ~urface which may have ~lip agent present after extrusion as a result of being subjected to aging or physical contact with a second surface containing one or more slip agent components. As hereinafter discussed, slip agent may be present ln the write-on compositions of this invention as a result of migration from coextrusion with a second plastic material or by contacting the write-on surface with a second plastic material containing slip agent, whereby slip agent is transferred to the write-on surface as a result of migration or simple physical contact of the second plastic material with the write-on composition.
As aforementioned, slip agent may be present at the write-on surface as a result of migration through the write-on composition from an adjacent material (commonly referred to as "blee~ing~ to the surface).
Although the exact mechanism by which the selected particulate material provides a further reduction in interference of slip agent with surface writability over that observed by use of the instant write-on composition without a particulate material to provide an improved write-on surface is unclear, it has been observed that when the selection of the particulate material is properly correlated to the selected slip agent(s) that improvement in the writability of the aged, corona-discharge treated write-on surface is observed. This improvement is particularly beneficial when the write-on composition is a layer of a multilayer film formed as part of a bag body -having a slip agent-containing bag film adjacent (in physical contact with) the write-on film composition as a coextruded multilayer film. This improvement in writability of the aged write-on surface has been obversed to be quite dramatic for a write-on film coextruded with a ~lip-containing bag film when the coextruded material undergoes aging at temperatures above room temperature, i.e., above about 80-F.
Since it is quite common during storage and ~hipment of bag and film products for such to be subjected to above room temperature for extended periods of time, this ability to retain writability after being subjected to such temperatures is an important write-on characteristic of the instant write-on compositions.
Particulate materials for use with various slip agents (including ecuramide) include: a fine particulate silica sold under the Trademark SYLOID~
and characterized as a particulate silica having a surface area of about 350 square meters per gram (m2/g), an average particle size of about 3.0 microns and a density of about 8 pounds per cubic foot (lbs/ft3); and calcium carbonate. It is believed that other suitable particulate silicas having surface areas between about 250 m2/g and 450 m2/g and average particle ~izes between about l and about 5 microns may be employed. A particulate calcium carbonate found useful herein is a particulate calcium carbonate characterized by a particle distribution between about 2 and about 5 microns with 50 percent of the particles less than 2 microns and 30 percent of the particles less than 1 micron. The particulate material is beneficially selected to have irregularly shaped particles and have particles resistant to crushing during the process of writing upon the write-on surface with a - 203~B7 pen. O~e calcium carbonate found useful in the instant invention is OMYACARB FT which is disclosed to be a fine wet ground, surface treated calcium carbonate (CaC03) cpecifically applicablé
for use in polyolefin films and having a mean particle diameter of 1.8 micron~ with a coarse fraction (top-cut) of 8 microns. Technical information on OMYACARB CaC03 i~ available from OMYA in Technical Bulletin No. US-PL-3, entitled, "OMYACARB CaCO3 MINERAL ADDITIVES IN POLYOLEFI~
FILMS "
Another calcium carbonate employable herein is Gama-Sperse CS-ll available from Geroga Marble Company. Gama-Sperse CS-ll is disclosed to be a stearate surface modified calcium carbonate having a median particle size of 3.9 microns (with 0.005 percent retained on a No. 325 wet ~creen) and a stearate content of 1.0 percent. Other particulate materials may be employed as filler~ and the like as second particulate materials including 6ilicas, talc, titanium dioxide, ~tarch and mixtures thereof.
The particulate material is typically present in an effective amount, as above discussed, and i~
typically present in an amount between about 3.0 and about 20.0 weight percent, preferably between about 5.0 and about 10.0 weight percent based on t~e total weight of the write-on composition, including the polymer components and various additi~es. ~he above "effective amount~ of particulate material is believed to be ~n effect~ve amount correlated to the amount of 61 ip agent present in most extruded or blown films, i.e., when the 61ip agent component is employed in an amount between ~bout 500 ppm (parts per ~illion) and about 2500 ppm (based on the total weight of the film composition) ~nd more typically in an amount between about 1000 ppm and about 2000 ppm.
When the write-on composition i8 a write-on film surface it is typically employed as a component of a larger article or film structure. Owing to the relative cost of the various plastic materials suitable for forming an article or film (e.g., polyethylenes, polypropylenes and the like), performance specifications for a selected product or other design parameters for a product, it is typically preferable to employ the write-on composition as a minor component of an overall structure, although the write-on composition may be used to form an article or film without other polymer components if such is desired. The cost of doing such is rarely justified, unless the entire surface is to be a write-on surface. In a broad sense, when the write-on composition is formed as a write-on film it may be used in conjunction with any article or other surface to which it may be affixed by adhesive, thermal or other suitable chemical or physical bonding means. When the write-on composition is formed into a film it may be advantageously employed as a write-on area, e.g., a stripe, on a bag body and, further may be provided as a coextruded or blown film component formed adjacent the film comprising the bag body. The final film composite will be a multilayer film structure wherein the write-on film is one layer and the bag film i8 a reconA layer.
Alternatively, the write-on film may be extruded as a second layer on an already formed bag film forming at least a two-layer multilayer structure or, alternatively, may be provided as a separate component by suitable bonding to a previously formed bag film or an article.
In one embodiment a write-on film is provided as a component of an overall film structure for use in bag manufacturing. In this embodiment a write-on film surface is provided in conjunction with a bag film ~tructure which may be employed for manufacturing a wide variety of bags heretofore known in the art, including pouch-type bags, disposer-type bags, handle-type bags, utility-type bags, drawstring-type baqs, food ~torage bag~, sandwich bags, various types of closure-type bags and the like. Representative of drawstring bags wherein a write-on surface may be provided are disclosed in U.S. Patent Nos. 3,414,032; 3,506,048; 3,687,357;
In addition to the patent literature, there is a significant body of non-patent, technical literature on corona-discharge treatment of plastic films. For example, the article "corona-discharge Treatment of Polyethylene Films I, Experimental Work and Physical Effects", Polymer engineering and Science, Vol. 18, No. 4 (March 1978) discusses the adhesion characteristics of corona-discharge treated polyethylene films and describes several testing procedures found useful in testing polyethylene films. Interestingly, the corona-discharge treated 2~30~67 films tested by the article's author were limited to unmodified polyethylene films (nbarefoot resins") and polyethylene films containing only low to medium concentrations of the slip additive commonly employed in the manufacture of polyethylene films.
The article reported some interesting results. The presence of 81 ip additive in the polyethylene film was noted to decrease the adhesion properties of the corona-discharge treated film, i.e., the treated film demonstrated reduced adhesion characteristics.
Significantly higher corona-Ai~chArge treatments were required to increase the surface adhesion properties. Further, the article reported that the addition of slip additives drastically changed both the polar characteristics and dispersion characteristics of the film's surface energy. The article noted that corona-discharge treatment of the slip additive (commonly referred to as "slip agents") associated with the polyethylene films did not result in an improvement in the "Wipe" test or "Adhesion" test employed in the article for evaluating the surface adhesion characteristics of the films. These tests are commonly employed to evaluate the writability/printability of a corona-discharge treated film surface as a function of the surface adhesive properties of the film surface (often referred to as the "wetting"
characteristics of the film surface by an ink).
Wetting characteristics of polyethylene films and the ability of such ~urfaces to have an ink adhere thereto have been di~cllc~e~ in the article entitled, "SURFACE CHARACTERIZATION OF CORONA
TREATED POLY~lnY~ENE FILMS", ANTEC 85, pages 269-272 (1985). This article examined the printability of polyethylene film and the effect of corona-discharge surface treatment on the polyethylene film surface 20~Q867 to improve ink wetting of the film surface, i.e., surface adhesion properties. The results reported by this article are interesting in many respects.
The author reported that, "Surface roughness is a barrier to wetting and yields higher than expected [contact~ angles" for unmodified low density polyethylene films (nbarefoot resins"), i.e. a polyethylene film not contAining slip or other processing additives. As expected, the author reported a clear relationship between the surface oxidation resulting from corona-discharge treatment and surface wetting of the evaluated barefoot polyethylene resins.
In another recent article entitled, "The Whole Story: Wettability, Corona Treaters and Compliance~
CO~v~ G MAGAZINE, September, (1986), the use of corona-discharge treaters is discussed in relation to in-line printing presses. The article is interesting in both its discussion of the effect of slip additives and use of water-based printing inks. The presence of slip additives on the surface of a modified film, i.e., slip additive-containing film, and the problems 81ip additives create in printing on the film surface are discussed. The author (Collins) reported interesting observations on the relationship of slip additives and the effect of corona-discharge treatment on slip additive-containing film. Several phenomena relating to the 61ip additives are discussed in the article, wherein Collins stated:
"It was observed that slip additives have a relatively low melt temperature. This means that subjecting the slip to excessive power levels would cause the slip additive to melt and become mobile, thereby obliterating the results of the treatment.
Corona treatment is strictly a surface phenomenon, he explained, with depth of 2~30867 penetration measured in angstroms. Whereas the surface slip additives can be El~ccescfully treated, subsequent movement through melting can cause the effect to be lost. Melt temperature of the slip, according to Pilla~
tests, appears to be in the neighborhood of 180- F."
After acknowledging the aforementioned phenomena the author ~i~c~c^e~ various alternatives to consider to resolve the problems encountered with slip additive-containing films. The thrust of the ensuing discussion related to adjustment of the corona-discharge treater and the role of the electrode and carrier roll in achieving optimum treatment results. (It is noted that the content of the article demonstrates that the author did not consider modification of the film composition as a means to improve the writability of the slip-additive-containing film.) Although the patent and non-patent literature contain numerous references to both chemical and physical treatments of a plastic surface for the purpose of improving the adhesion characteristics of a film, e.g. the adherence of an ink to the plastic surface, there has been relatively little prior art discussion on the importance of the chemical composition of the plastic material being treated.
Two patents discussing the composition of the plastic material as a means for affecting the adhesion characteristics of a plastic surface are disc~ e~ hereinafter.
An early reference to a plastic drawing material sheet is found in British Patent Specification No. 1,478,474. This British Patent discloses a plastic sheet material having a drawing layer which contains a crosslinked thermoplastic film-forming binder comprising more than 50% by 2030~67 weight of a polyvinyl butyral crosslinked by means of an etherified (polymethyl)-melamine in the presence of an acid catalyst, which polyvinyl butyral contained at least 18 per cent by weight of vinyl alcohol y~OU~3 before crosslinking. The British patent discloses the drawing layers as suitable for use with graphite pencils and ink. In addition, the drawing layers can contain ~toothing agents" selected from a wide range of particulate materials, including diatomaceous earth, glass powder, titanium dioxide, zinc oxide, kaolin and amorphous silica. The function of the "toothing agents" is somewhat unclear from the British patent, although the patentee states that a mixture of two toothing agents having different particle size and specific surface may be provided to improve the erasability of the drawing layer. One would assume that an improvement in erasability corresponds to a decrease in surface adhesion or a decrease in surface writability.
U.S. Patent No. 4,801,487 discloses an imprintable sheet of a plastic comprising a carrier sheet and a coating layer applied on at least one layer of the carrier sheet for receiving an imprint. The coating layer to be imprinted consists of a firm polymer matrix and microporous finely divided solid particles. The patentee describes the non-imprintable carrier sheet as a non-polar polymer such as polyethylene or polypropylene. The firm polymer matrix of the coating layer is disclosed at column 3, lines 30-39 as consisting substantially of several polymers. These polymers are contrasted by the patentee with the polyethylene and polypropylene polymers employed for forming the non-imprintable carrier sheet. For example, the firm polymer matrix (the coating layer to be imprinted) may be selected -2~3~8~i7 from a large class of polymers, including polyacrylates, polymethacrylates, polyesters, polystyrenes, poly-1-3-dienes, polyamides, polyurethanes, polyvinyl butyral, polyvinyl acetate alkyde resins, urea resins and resins modified with natural materials such as starch and casein. The "microporous finely divided solid particles" are disclosed as absorbent solid particles and are di~-c~s~e~ at column 3, lines 40-60. The extensive list of absorbent solid particles covers a wide range of solid materials having widely different chemical and physical properties, including white pigments and white or colorless fillers, such as aluminum oxide, barium sulfate, titanium dioxide, silicic acid, silicates, chalks, starch, melamine resins and/or formaldehyde resins. The function of the microporous finely divided solid particles cannot be surmised from this diverse random listing of materials. In fact, the patentee points out that the relevant criteria in selecting the microporous finely divided solid particles are that the particles be finely divided (having large specific surface area) and have a microporous internal structure. (See: column 3, lines 50-53) The specification and examples refer to the application of the firm polymer matrix as being a "coating"
applied on the non-imprintable carrier ~heet. The patentee actually refers to the firm polymer matrix coating as a "liguid primer". It is clear that the patentee's imprintable coating layer is related only to the firm polymer matrix with the microporous finely divided solid particles wherein the coating is applied as a liquid primer coating to a non-imprintable carrier sheet, e.g., a polyethylene or polypropylene film. The patentee discloses a corona-discharge treatment of the carrier sheet -before the primer liguid is applied. It is clear that the corona-discharge treated carrier sheet is not considered to be a write-on surface, (i.e., the coating provides this function) but is merely treated to improve adhesion of the liquid primer to the carrier sheet.
The addition of calcium carbonate additives for polyolefin films has been reported in the prior art. For example, the use of OMYACARB~
(OMYACARB CaC03 is sold by OMYA, 61 Main Street, Proctor, Vermont 05765) calcium carbonate mineral additive as a mineral additive in polyolefin films has been disclosed by the manufacturer to reduce the corona-discharge treatment levels by over 50 percent. Further, in sales literature on OMYACARB calcium carbonate mineral additive, it is noted that "Early studies also indicate that the decay of Corona Treatment over time is minimized by the inclusion of a calcium carbonate mineral additive. It is believed that the microroughening effect on the film surface that is imparted by these mineral additives allows the reduction in Corona level and the blockage of decay. It is important to note also that this micro-roughening effect enhances film printability. n The above discussion is instructive in demonstrating that the prior art to date has not appreciated the complexity of the problems associated with write-on plastic surfaces as such relate to compositional changes in the formulation of the plastic material. These problems (such problems not heretofore appreciated by the prior art) are further complicated when the user is attempting to write on a plastic film surface manufactured in conjunction with a commercial bag manufacturing process. It has been observed herein .
that additional problems arise in commercial bag manufacturing proces~Qs owing to the numerous and variable manufacturing parameters of these processes. For example, it is common practice to employ a number of chemical processing aids to assist in commercial manufacturing proceC~^A for bags and film products. Such additives are typically provided as a "masterbatch" to the plastic material being processed. For example, a common additive in the masterbatch is a slip additive (commonly called a "slip agent"). The slip agent is added to improve machine handling of the plastic material, e.g., a plastic film, by increasing the slipperiness of the surface of the plastic so as to facilitate its ease of passage through the manufacturing eguipment. The very slipperiness that is beneficial in the manufacture of the plastic material has been found to be detrimental to the end user's ability to write on the plastic film surface. The deterioration in the printability of the film as a result of film additives and/or oligomers is addressed in U.S. Patent No. 4,832,772 wherein a physical surface "wiping" step in employed and is preferably employed with a preparatory solvent treatment of the surface. U.S. Patent No.
4,832,772 discloses a process for wiping off a weak lay on the film surface containing oligomers and additives, although, surprisingly, no discussion of the nature of the "additives" is provided by the patentee.
As aforementioned, the use of a corona-discharge treatment of a plastic surface has been generally found to improve the writability or printability of slip agent-cont~in;ng plastic materials by oxidizing the film surface and, if slip agent is present, "burning-off" a portion of the ..~
slip aqent on the film surface. A discussion of the effect of corona~ chArge treatment is set forth in the recent article by James F. Carley and P. Thomas Kitze, entitled, "Corona-DiE^h~rge Treatment of Polyethylene Films. I. Experimental Work and Physical Effects", POLYMER ENGT~ T~G AND SCIENCE, Vol. 18, No. 4 (March, 1978). The article is instructive in its disclosure that no changes in surface topography as a result of commercial corona-discharges are believed to contribute to practical adhesion phenomena and, further, that very high corona-di~ch~rge treatment was required to affect slip additives at the surface of polyethylene It has been found herein in accordance with the instant invention that this "burning off" effect and the associated improvement in surface adhesion characteristics is a short-lived surface effect when slip agent is present in the plastic composition or in close proximity to the plastic composition. This observation stems from the fact that corona-discharge is a surface treatment. The slip agent present in the bulk plastic composition is not affected by the corona-discharge treatment. It has been observed that this "bulk" ~lip agent in the plastic composition migrates to the corona-discharge treated surface as time passes, i.e., as the film ages, and the amount of slip agent at the surface increases with time. Thi~ naging phenomenon" is related to the time the film has aged as well as the ambient conditions, e.g., temperature, under which the film has aged. Further, during many manufacturing proces~^~, e.g., during the manufacturing of plastic bags and plastic films, the plastic bags and plastic films are stacked or placed on a roll in such a manner that film ~urface treated by corona-discharge contacts an untreated film 2030~67 ..
surface having a greater amount of slip agent on the film surface that i6 present on the corona-discharge treated film surface. Once again, the net result of this contacting is an increase in amount of slip agent on the corona-~i~chArge treated film surface as a result of the physical contacting of the two film ~urfaces.
The prior art has not appreciated and, accordingly, has not addressed the aforementioned problems associated with write-on plastic surfaces.
Further, the unique problems associated with write-on surfaces associated with plastic bags has not been appreciated as to the unique problems associated with bag surfaces in physical contact with slip agents. As a result of this lack of appreciation, the prior art has not proposed effective means by which the write-on characteristics of plastic surfaces may be improved other than by simple mechanical or chemical surface treatment which are not effective for plastic surfaces that have undergone aging in the presence of slip agents.
The instant invention addresses these problems by providing a write-on composition suitable for corona-discharge (or other surface treatment providing a similar surface treating effect) having improved resistance to 61ip agent interference with the writability of the write-on film ~urface.
Further, the instant invention addresses the unique problems associated with the commercial manufacture of plastic bags having a bag body formed from a plastic film containing at least one slip agent component and having at least one write-on surface on at least one wall of the bag body.
D-lSS84 ~ 2~3~867 SUMMARY OF THE lNv~NllON
The instant invention relates to a writable plastic surface (preferably a plastic film surface) formed by corona-~isrhArge treatment (or other similar surface modification treatment) of a novel write-on composition. The write-on composition to be treated is characterized as comprising: a) a physical mixture of two polymers, as described in detail hereinafter; and, optionally, but preferably, b) particulate material present in an effective amount to further improve the writability of the corona-discharge treated plastic surface.
In one embodiment the write-on surface comprises a corona-Ai~c~rge treated write-on film composition wherein the write-on film composition, preferably sans slip agent, is coextruded with a bag film containing a slip agent, preferably a polyethylene film. A particulate material may be present in an effective amount in the write-on composition to aid in a reduction in the detrimental effect of slip agent on the writability of the corona-discharge treated writable film surface. The write-on film surface may also be beneficially provided with an embossed pattern.
In a further embodiment the write-on composition to be corona-discharge or surface treated is formed as a film which i8 substantially sans slip agent, i.e., formed substantially in the absence of slip agent or contains no slip agent additive. In this embodiment the write-on composition may be associated with a bag body and formed as a layer in a co-extruded ~lip agent-containing bag film.
In a further embodiment the write-on composition comprises a ma~or amount of polyolefin resin, e.g., polypropylene, high density polyethylene and/or low density polyethylene, as the first polymer and a minor amount of a polyisobutylene polymer as the second polymer, as hereinafter ~;c~ ced.
In a further embodiment the invention relates to a bag having a write-on surface and to a stack of bags with a write-on surface.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a 200 X photomic~o~aph illustrating a film surface not of the instant invention showing a non-wetting surface when the film surface is not corona-discharge treated.
FIG. 2 is a 2000 X photomic~o~aph illustrating a portion of the film of FIG. 1.
FIG. 3 is a 200 X photomi~Loy~aph illustrating a portion of a film the same as shown in FIG. 1 but corona-discharge treated at 63.8 watts per square inch.
FIG. 4 is a 2000 X photomi~oyLaph illustrating a portion of the film of FIG. 3.
FIG. 5 is a 200 X photomic~oy~aph illustrating a film surface containing a non-wetting surface having an embossed surface, no slip agent and which has not been corona-discharge treated.
FIG. 6 is a 2000 X photomi~Gyraph illustrating a portion of the film of FIG. 5.
FIG. 7 is a 200 X photomi~o~aph illustrating a film surface of a write-on film (containing a polyisobutylene component according to the instant invention) before corona-discharge treatment.
FIG. 8 is a 2000 X photomic~oy~aph illustrating a portion of the film of FIG. 7.
FIG. 9 is a 200 X photomic~o~Laph illustrating the same film surface depicted in FIG. 7, except the surface has been corona-di~chAFge treated at 63.8 2~asG7 watts per square inch.
FIG. 10 is a 2000 X photomicrograph illustrating a portion of the film of FIG. 9.
FIG. 11 is a 200 X photomic.oyLaph illustrating a film cont~ini~g 3000 ppm 61ip agent and a TiO2-containing white masterbatch with 10 weight percent of a SYLOID~ particulate ~ilica which has not been corona-~i~ch~rge treated.
FIG. 12 is a 2000 X photomic~GyLaph illustrating a portion of the film surface depicted in FIG. 11.
FIG. 13 is a 200 X photomic~oyLaph of the film shown in FIG. 11 which has been corona-discharge treated at 44.6 watts per square inch (watts/in2).
FIG. 14 is a 2000 X photomi~LG~Laph illustrating a portion of the corona-~i~ch~rge treated film surface depicted in FIG. 13.
FIG. 15 is a 2000 X photomic.o~aph illustrating a portion of the film surface depicted in FIG. 16.
FIG. 16 is a 200 X photomic~oyLaph illustrating a film containing and a TiO2-containing white masterbatch with 10 weight percent SYLOID~
particulate silica and which was corona-discharge treated at 46.6 watts per square inch.
FIG. 17 is a 200 X photomi~Lo~Laph illustrating a film surface of a write-on film containing a polyisobutylene component, 1000 ppm 61ip agent, 5000 ppm Super Floss~, and 4.5 wt. % of a white masterbatch, and which was corona-discharge treated at 44.6 watts per square inch.
FIG. 18 i6 a 2000 X photomic~cy.aph illustrating a portion of the film ~urface depicted in FIG. 17.
FIG. 19 i6 a 200 X photomicLoyLaph illustrating a film surface of a write-on film containing a 2030~7 polyisobutylene component (~Xx~T~R~ PA-30) with 10 weight percent SYLOID~ particulate silica and which was corona-~i~chArge treated at 44.6 watts per square inch.
FIG. 20 is a 2000 X photomi~Gy.aph illustrating a portion of the film ~urface of FIG.
19 .
FIG. 21 i8 a 200 X photomicLGyLaph illustrating a film surface of an aged write-on film according to the invention containing a polyisobutylene component, a SYLOID~ particulate silica and which was not corona-discharge treated.
FIG. 22 is a 2000 X photomic}o~aph illustrating a portion of the film surface depicted in FIG. 21.
FIG. 23 is a 200 X photomic~o~Laph illustrating a film similar to that shown in FIG. 21 except that ~Xx~T~R~ PA-30 was replaced with ~Xx~roR~ PA-50.
FIG. 24 is a 2000 X photomi~L~yLaph illustrating a portion of the film surface depicted in FIG. 23.
FIG. 25 is a 200 X photomic~.aph illustrating the film depicted in FIG. 21 after being aged at 140 degrees F for 28 days.
FIG. 26 is a 2000 X photomicLG~Laph illustrating a portion of the aged film of FIG. 25.
FIG. 27 is a 200 X photomic~yLaph illustrating the film depicted in FIG. 23 after being aged at 140 degrees F for 28 days.
FIG. 28 is a 2000 X photomi~L~yLaph illustrating a portion of the film surface depicted in FIG. 27.
FIG. 29 is a 200 X photomic~y~aph illustrating a portion of a low density polyethylene film surface containing a 10 wt. % of polyisobutylene component and 5 wt. % calcium carbonate component.
FIG. 30 is a 2000 X photomi~LGy.aph illustrating a portion of the film ~urface of FIG. 29.
FIG. 31 is a 200 X photomi~Gy~aph illustrating a portion of the film surface of a film similar to that shown in FIG. 29, except 20 wt. % of the polyisobutylene component was employed.
FIG. 32 is a 2000 X photomi~o~Laph illustrating a portion of the film surface of FIG. 31.
FIG. 33 is a 200 X photomiclG~Laph illustrating a portion of the film surface similar to that shown in FIG. 29, except 10 wt. % calcium carbonate was employed.
FIG. 34 is a 2000 X photomic~oyraph illustrating a portion of the film surface of FIG. 33.
FIG. 35 is a 200 X photomic,oy~aph illustrating a portion of the film surface similar to that shown in FIG. 29, except 20 wt. % of a polyisobutylene component was employed and 20 wt. % calcium carbonate was employed.
FIG. 36 is a 2000 X photomic~G~aph illustrating a portion of the film surface of FIG. 35.
FIG. 37 is a perspective view of a flexible container including a write-on surface in accordance with the invention and an optional reclosable fastening device.
FIG. 38 is a perspective view of the sidewall of a flexible container showing a write-on stripe coextruded with a bag film.
DETAILED DESCRIPTION OF THE 1NV~N1~1ON
In its broadest sense the invention relates to a writable plastic surface suitable for use as a write-on or an imprintable surface. The ability of a plastic surface to accept an ink, e.g., from an ink pen or an ink printing process, is generally referred to herein as the "writability" or the "write-on" characteristic of the plastic surface and reference to a "write-on" surface herein includes the application of ink to a surface by use of a ballpoint pen, a printing process or other means known in the prior art. The instant invention relates to a writable plastic surface derived by corona-discharge treatment (or other similar physical or chemical surface treatment) of a write-on composition. The write-on composition to be treated is generally characterized as: a) a physical mixture of two substantially incompatible polymers; and, optionally, b) a particulate material present in an effective amount to improve the writability of the corona-discharge treated film surface. The use of so called "corona-discharge treaters" to treat plastic surfaces is well known, as evidenced by articles such as "The whole story: wettability, corona treaters and compliance", CONVERTING MAGAZINE, September 1986.
In one embodiment the write-on composition may contain a slip agent and is formed into a film but is preferably sans slip agent. The film surface is corona-discharge treated to provide a write-on film surface having improved writability upon aging.
In a further embodiment a write-on film is coextruded with a polyolefin film, e.g., a polyethylene film, containing a slip agent and the write-on composition is provided as a write-on surface sans slip agent. Further, a particulate material may be present in an effective amount to interfere with the negative affect that migrating slip agent has on the writable film surface as the film ages. As discussed hereinafter the presence of slip agent in the polyolefin bag material and write-on stripe portion of a bag decreases the writability of the write-on surface, especially as the film undergoes aging after its manufacture. In a further embodiment the write-on ~urface is a film comprising a major amount of a mixture of low density polyethylene and high density polyethylene as a first polymer and a minor amount of a polyisobutylene as the second polymer, preferably provided as a polyisobutyler.e ~GI.~aining material such as ~x~ToR~ PA-30 or ~xx~T~R~ PA-S0, as hereinafter discl~cse~.
The invention also relates to a bag having a write-on surface, a stacked bag article comprising a plurality of bags having a write-on surface, e.g., a write-on stripe.
Although corona-discharge treatment has generally been found to be useful in improving the write-on characteristics of a plastic surface, including plastic film surfaces, it has been observed herein that corona-discharge treatment alone is not suf-ficient to provide an acceptable write-on surface for many end use applications.
This writability problem becomes especially acute when the write-on surface of interest is provided on a bag body formed from a thermoplastic film formed with a slip additive. The presence of the slip agent has been observed to be an especially acute problem as the film ages, since slip agent has been observed to bleed to the film 6urface. Further, the rate of bleeding of the slip agent to the film surface has been observed to increase with increasing temperature. The write-on characteristics of a write-on area are even further complicated when the write-on area is provided as a write-on area manufactured in conjunction with heretofore commercially employed bag manufacturing proc~Cces. The unique problems associated with write-on surfaces and bag manufacturing will be discussed hereinafter in conjunction with one embodiment of the instant invention.
The write-on composition of the instant invention is generally characterized as comprising two polymers wherein the second polymer is substantially incompatible in the first polymer.
The term "substantially incompatible" is used herein to denote a polymer mixture wherein at least one polymer component forms identifiable particles in the polymer mixture when the polymer mixture is extruded as a film composition. In one embodiment of tbe instant invention the write-on composition comprises a major amount of a low density polyethylene and a minor amount of a polyisobutylene-containing polymer blend. Two such polymer blends found to be useful in the instant invention are sold by Exxon Chemical Company, P.O.
Box 3272, Houston, Texas, 77253-3272, under the product trade designations ~xx~TOR~ PA-30 and ~X~TOR~ PA-50. ~X~TOR~ PA-30 is a pelletized polyisobutylene alloy and modifier comprising a blend of polyisobutylene and polypropylene in a weight ratio of about 1 to 2, respectively. Typical properties of T~XX~TOR~ PA-30 are as follows:
EXXELOR~ PA-30 Property Value ASTM Method Melt Index(l90-C), g/lOmin 0.15 D1238(Condition E) Melt Flow Rate (230-C),g/lOmin 0.50 D1238(Condition L) Density,g/cc 0.91 D1505 Vicat Softening Point(200g),-F 310 D1525 Hardness (5sec, Shore A) 85 D2240 Flexural Modulus, psi 6,150 D790 ~xx~ToR~ PA-50 is a pelletized elastomeric concentrate comprising a blend of a polyisobutylene and a high density polyethylene in a weight ratio of about 1 to 2, respectively. Typical properties ~XX~T~R PA-50 are as follows:
~X~T~R~ PA-50 ProDerty Value ASTM Method Melt Index(l90-C), g/lOmin 0.23 D1238(Condition E) Melt Flow Rate (230-C),g/lOmin 0.65 D1238(Condition L) Density,g/cc 0.924 D1505 Vicat Softening Point(200g),-F 253 D1525 Hardness (5sec,Shore A) 78 D2240 Flexural Modulus, psi 6000 D790 The first polymer of the write-on composition is typically a polyolefin, e.g., polyethylene, polymer (including ultra-low density, low density, medium density and high density) owing to their low cost but may be other polymeric materials heretofore known in the art. The first polymer may be selected from a wide range of polymers including polyethylenes, polypropylene, polybutylenes, butadiene/styrene, polyvinyl alcohol and the like.
Further, the first polymer may comprise a homogeneous blend of one or more polyethylene polymers and one or more other polymers, e.g., it has been observed that a first polymer comprising a mixture of low density polyethylene and a polyvinyl alcohol or a butadiene/styrene polymer may be useful as the first polymer in the two polymer mixture of the write-on composition. The use of a polyvinyl alcohol or butadiene/styrene as a component in a mixture with polyethylene is believed to sequester the migration of 61ip agent, although the mechAnism of the interaction of the 61 ip agent and the polyvinyl alcohol or butadiene/styrene is not understood at present.
The second polymer is preferably a polyisobutylene polymer (including physical mixtures of polyisobutylene with polypropylene, the various polyethylenes and the like) when the first polymer is a polyolefin, although other substantially incompatable polymers may be employed. As aforementioned, the operative parameter is selecting the first and ~ec~nA polymers is the substantial incompatibility of the -~conA polymer in the first polymer, as herein described.
The write-on composition may also contain a particulate material to improve write-on characteristics, especially when the write-on film undergoes aging. The particulate material is present in an effective amount to reduce interference of the slip agent at the write-on surface as compared to the writability that would be observed if the particulate material were not present in an effective amount. The role of the particulate material in the improvement of the writability of the write-on surface is believed to result from several factors. Although not wishing to be bound by any theory, it is believed that when properly selected the particulate material will provide two distinct functions. First, the particulate material may interact with the slip agent to inhibit its migration i.e., bleeding, to the write-on surface. Second, the particulate material may act as a ro~g~ing agent for the write-on surface. This roughening effect may provide several advantages peculiar to the adherence of ink to the surface by use of an ink pen as opposed to printing on the ~urface. Since the slip agent may collect in small pits formed by several particles of the particulate material, the slip agent may be below the ~urface of the write-on surface over which the ink is contacted and, accordingly, does not interfere with the writability of the write-on surface. Further, the "roughness"
--- 2~30867 characteristic of the particulate material is also believed to be beneficial when the write-on surface is written upon with a ballpoint pen, since the roughness of the surface is believed to beneficially aid in the mechAn~cal rolling of the ballpoint pen as it moves across the write-on 6urface. Further, the use of a particulate solid, such as calcium carbonate, may act as a cleaning aqent for the ball point of the pen to assigt in dislodging 61ip agent picked up by the pen during writing. It has been observed that not all particulate materials are useful, since use of talc was not observed to p~ovide a beneficial improvement in the writability of the write-on surface.
The selection of the first polymer and second polymer is related to the substantial incompatibility of the second polymer in the first polymer. The first polymer and cecon~ polymer are selected such that identifiable particles of the second polymer are present in the first polymer.
FIGS. 1 to 36 in the instant application demonstrate the identification of the second polymer particles by use of an electron sc~nning microscope. Although the relative amount of the first polymer and the second polymer will be related to the aforementioned substantial incompatibility, the first polymer will typically be present in a major amount (i.e., over fifty percent (50%) by weight) of the write-on composition. The secon~ polymer will typically be present in a minor amount (i.e., less than fifty percent (50%) by weight) of the total write-on composition.
It has been found that when the first polymer is a low density polyethylene having a density between about 0.915 to 0.940 (of the type commonly employed in the manufacture of thermoplastic bags and film) and/or polypropylene and the second polymer is a polyisobutylene-containing material such as ~Xx~T~R~ PA-30 or ~xxFT~R~ PA-50, that the aforementioned "substantially incompatible"
criteria are met. In one embodiment a low density polyethylene (formed with a l-butene, l-hexene or l-octene comonomer) having a density of between about 0.915 and about 0.940 g/cm3, preferably between about 0.915 and about 0.930 g/cm3 (typically having a melt index of between about 0.6 to 1.2) is employed at between about 50 wt. % and about 95 wt. % of the write-on film composition and a polyisobutylene/polypropylene mixture (sold under the Trademark ~xx~T~oR~ PA-30 by EXXON Chemicals Company) or a polyisobutylene/high density polyethylene mixture (sold under the trademark ~xx~ToR~ PA-50 by Exxon Chemicals Company) comprises between about 5 and about 20 weight percent of the write-on composition. The aforementioned discussions on the substantial incompatibility of the second polymer in the first polymer do not include any other polymer present in a polymer blend, unless such polymer(s) also meets the aforementioned criteria of substantial incompatibility, i.e., the first polymer and/or second polymer may themselves each comprise more than one polymer component. With respect to the use of ~xx~T~R~ PA-30 and ~xx~T~R~ PA-50 as the second polymer component it has been observed that the polypropylene and the high dénsity polyethylene present as carrier polymers for the polyisobutylene polymer in the ~xx~T4R~ PA-30 and ~Xx~TnR~
PA-50, respectively, do not meet the compatibility requirements for a second polymer when the first polymer i6 selected to be a low density polyethylene and, therefore, such carrier polymers should be 20~0867 treated as first polymer components in determining the relative weight percents of the first polymer and second polymer.
In one embodiment a polyisobutylene-containing material is employed as a component of the write-on composition (~X~T~R~ PA-50) and is present as a minor amount of the write-on composition with the major component comprising a low density polyethylene. Since ~xx~r~R~ PA-50 (and ~Xx~oR~
PA-30) is a polymer mixture (containing about 67 weight percent polyisobutylene and 33 weight percent of a high density polyethylene), the overall weight percent of polyisobutylene polymer in the write-on composition will generally be between about 3.25 weight percent and about 13.0 weight percent polyisobutylene, based upon the total weight of the polymeric components (e.g., polyisobutylene, low density polyethylene and high density polyethylene) in the write-on composition. In general the preferred low density polyethylene material employed as the major component with the aforementioned minor component (polyisobutylene-containing material) is characterized as having a density between about 0.915 and about 0.940 g/cm3, preferably between about 0.915 and about 0.930 g/cm3, and also typically characterized by a melt index of between about 0.6 and about 1.2. Further, when the write-on composition is one layer of a two-layer coextruded film structure, wherein the other layer is a slip agent-containing low density polyethylene bag film (routinely containing between about 500 ppm and about 2500 ppm elip agent, e.g., a C18 to C22 fatty acid amide, ~uch as ecuramide), it has been observed that it is preferred to have the write-on film comprise greater than about 30 percent of the combined total thickness of the write-on film and bag - 2030~67 film, preferably greater than 50 percent of the combined thickness. It has been observed that by making the thick~esR of the write-on film layer greater than about 30 percent of the total multilayer film thickness that the amount of slip agent which will bleed from the underlying slip agent-containing bag film to the write-on film ~urface is beneficially controlled, whereby the writability of the write-on surface is improved. Reference i~ made to FIG. 38 wherein a perspective view of such a multilayer, coextruded film is shown.
As aforementioned, the write-on composition may alæo contain a particulate material to improve the writability of the composition, when the write-on composition contains or is adjacent a material containing a slip agent. It has been observed that by providing an effective amount of a particulate material, i.e., an amount effective in reducing the detrimental effect of slip agent on writability of the surface of an article or film formed from the write-on composition, that the writability of the write-on surface as it ages is improved, as compared to the writability on the surface if the particulate material is not employed in an effective amount.
Although, the selection of the particulate material and its relationship to the first polymer and second polymer is not fully understood, the selection is believed to be related to the ability of the selected particulate material to chemically and/or physically interact with a selected slip agent whereby the detrimental effects of slip agent on surface writability is decreased as a result of the addition of the particulate material to the write-on film composition.
One or more slip agents, e.g., preferably one or more C18 to C22 fatty acid amides, may be used in 2030~67 the bag film and the write-on composition, although it is preferred that no slip agent be employed in the write-on composition i.e., the write-on composition is preferably sans 81ip agent. This reference to "sans slip agent" refers to the write-on composition as formed, e.g., as extruded, and not to the write-on ~urface which may have ~lip agent present after extrusion as a result of being subjected to aging or physical contact with a second surface containing one or more slip agent components. As hereinafter discussed, slip agent may be present ln the write-on compositions of this invention as a result of migration from coextrusion with a second plastic material or by contacting the write-on surface with a second plastic material containing slip agent, whereby slip agent is transferred to the write-on surface as a result of migration or simple physical contact of the second plastic material with the write-on composition.
As aforementioned, slip agent may be present at the write-on surface as a result of migration through the write-on composition from an adjacent material (commonly referred to as "blee~ing~ to the surface).
Although the exact mechanism by which the selected particulate material provides a further reduction in interference of slip agent with surface writability over that observed by use of the instant write-on composition without a particulate material to provide an improved write-on surface is unclear, it has been observed that when the selection of the particulate material is properly correlated to the selected slip agent(s) that improvement in the writability of the aged, corona-discharge treated write-on surface is observed. This improvement is particularly beneficial when the write-on composition is a layer of a multilayer film formed as part of a bag body -having a slip agent-containing bag film adjacent (in physical contact with) the write-on film composition as a coextruded multilayer film. This improvement in writability of the aged write-on surface has been obversed to be quite dramatic for a write-on film coextruded with a ~lip-containing bag film when the coextruded material undergoes aging at temperatures above room temperature, i.e., above about 80-F.
Since it is quite common during storage and ~hipment of bag and film products for such to be subjected to above room temperature for extended periods of time, this ability to retain writability after being subjected to such temperatures is an important write-on characteristic of the instant write-on compositions.
Particulate materials for use with various slip agents (including ecuramide) include: a fine particulate silica sold under the Trademark SYLOID~
and characterized as a particulate silica having a surface area of about 350 square meters per gram (m2/g), an average particle size of about 3.0 microns and a density of about 8 pounds per cubic foot (lbs/ft3); and calcium carbonate. It is believed that other suitable particulate silicas having surface areas between about 250 m2/g and 450 m2/g and average particle ~izes between about l and about 5 microns may be employed. A particulate calcium carbonate found useful herein is a particulate calcium carbonate characterized by a particle distribution between about 2 and about 5 microns with 50 percent of the particles less than 2 microns and 30 percent of the particles less than 1 micron. The particulate material is beneficially selected to have irregularly shaped particles and have particles resistant to crushing during the process of writing upon the write-on surface with a - 203~B7 pen. O~e calcium carbonate found useful in the instant invention is OMYACARB FT which is disclosed to be a fine wet ground, surface treated calcium carbonate (CaC03) cpecifically applicablé
for use in polyolefin films and having a mean particle diameter of 1.8 micron~ with a coarse fraction (top-cut) of 8 microns. Technical information on OMYACARB CaC03 i~ available from OMYA in Technical Bulletin No. US-PL-3, entitled, "OMYACARB CaCO3 MINERAL ADDITIVES IN POLYOLEFI~
FILMS "
Another calcium carbonate employable herein is Gama-Sperse CS-ll available from Geroga Marble Company. Gama-Sperse CS-ll is disclosed to be a stearate surface modified calcium carbonate having a median particle size of 3.9 microns (with 0.005 percent retained on a No. 325 wet ~creen) and a stearate content of 1.0 percent. Other particulate materials may be employed as filler~ and the like as second particulate materials including 6ilicas, talc, titanium dioxide, ~tarch and mixtures thereof.
The particulate material is typically present in an effective amount, as above discussed, and i~
typically present in an amount between about 3.0 and about 20.0 weight percent, preferably between about 5.0 and about 10.0 weight percent based on t~e total weight of the write-on composition, including the polymer components and various additi~es. ~he above "effective amount~ of particulate material is believed to be ~n effect~ve amount correlated to the amount of 61 ip agent present in most extruded or blown films, i.e., when the 61ip agent component is employed in an amount between ~bout 500 ppm (parts per ~illion) and about 2500 ppm (based on the total weight of the film composition) ~nd more typically in an amount between about 1000 ppm and about 2000 ppm.
When the write-on composition i8 a write-on film surface it is typically employed as a component of a larger article or film structure. Owing to the relative cost of the various plastic materials suitable for forming an article or film (e.g., polyethylenes, polypropylenes and the like), performance specifications for a selected product or other design parameters for a product, it is typically preferable to employ the write-on composition as a minor component of an overall structure, although the write-on composition may be used to form an article or film without other polymer components if such is desired. The cost of doing such is rarely justified, unless the entire surface is to be a write-on surface. In a broad sense, when the write-on composition is formed as a write-on film it may be used in conjunction with any article or other surface to which it may be affixed by adhesive, thermal or other suitable chemical or physical bonding means. When the write-on composition is formed into a film it may be advantageously employed as a write-on area, e.g., a stripe, on a bag body and, further may be provided as a coextruded or blown film component formed adjacent the film comprising the bag body. The final film composite will be a multilayer film structure wherein the write-on film is one layer and the bag film i8 a reconA layer.
Alternatively, the write-on film may be extruded as a second layer on an already formed bag film forming at least a two-layer multilayer structure or, alternatively, may be provided as a separate component by suitable bonding to a previously formed bag film or an article.
In one embodiment a write-on film is provided as a component of an overall film structure for use in bag manufacturing. In this embodiment a write-on film surface is provided in conjunction with a bag film ~tructure which may be employed for manufacturing a wide variety of bags heretofore known in the art, including pouch-type bags, disposer-type bags, handle-type bags, utility-type bags, drawstring-type baqs, food ~torage bag~, sandwich bags, various types of closure-type bags and the like. Representative of drawstring bags wherein a write-on surface may be provided are disclosed in U.S. Patent Nos. 3,414,032; 3,506,048; 3,687,357;
3,547,341; 4,629,654; and 4,664,6~9.
Representative of closure-type bags wherein a write-on surface may be provided are disclosed in V.S. Patent Nos.: Reissue Patent RE No. 28,969; 2,978,768; 3,038,225;
Representative of closure-type bags wherein a write-on surface may be provided are disclosed in V.S. Patent Nos.: Reissue Patent RE No. 28,969; 2,978,768; 3,038,225;
4,212,337; 3,363,345; 4,733,778; 4,736,450;
4,822,539; and 4,829,641.
When the closure bag is a color change closure bag as disclosed in U.S. Patent Nos.
4,363,345 and 4,829,641 it is preferred to provide the write-on ~urface on the 6idewall of the bag having the translucent closure element, although such is not required. By providing the write-on ~urface on the sidewall having tbe translucent closure element the user of the closure bag can first close the baq while observing the color change of the color change closure and then write on the wrlte-on surface without the necessity of turning over the bag to access the write-on 6urface. ~he embodiment wherein a write-on 6tripe i6 provided on a sidewall of a closure-ty~pe bag i6 ~hown in FIG. 37. FIG. 37 ~hows a typical flexible container 40 formed from a thin plastic film which bas been folded to define a bottom portion 41 and heat 6ealed along vertical edges 42 to form a pouch. The 6idewall6 43 extend beyond a closure device (optional) compri~ed of closure -203~867 elements 50 and 52 to provide flanges 45 and mouth portions 46 and 48 to simplify the opening and closing of closure elements 50 and 52. A write-on stripe surface 46 is provided according to the instant invention.
The term "film", as used herein and in the prior art, represents any three-dimensional material which pos~es~^s two opposite facing surfaces separated by edging surfaces. The opposite facing surfaces may be mono- or poly-planar and the combined surfaces typically (and preferably) poscess many times the area of the edge surfaces. The film, e.g., bag film, which may be employed with a write-on surface in the practice of the invention may be any film, including plastic, resin, metal, textile, fiber reinforced plastic or resin, ceramic, glass, rubber, paper and cardboard, wallboard, composites thereof, and the like to which the write-on film may be associated, e.g., affixed. The composite films may be employed to make bag structures. The films employed in the manufacture of bags are typically polyolefin thermoplastic films such as one or more layers of one or more of polyethylene (low density, high density, linear low density, ultra low density and/or combinations thereof), polypropylene, polyethylene copolymers (low density, linear low density, ultra low density, high density and/or combinations), polybutylenes, ABS polymers, polyurethanes, polycarbonates, polysulphones, aliphatic polyamides, polyarylamides, polyaryletherketones, polyarylimideamides, polyaryletherimides, polyesters, polyarylates, polyoxymethylene, poly(epsilon-caprolactone), and the like, alone or composited with a variety of materials, such as metal films, paper, cardboard, textile structures, wood, and the like.
2030~67 The write-on compositions of the instant inventions are preferably employed as films and may be extruded or blown, preferably extruded, using conventional manufacturing processes and parameters.
For example, the instant write-on compositions may be employed as an extruded write-on stripe on a thermoplastic film, e.g., a 0.5 to 1 inch wide stripe. When the film is employed to form a bag the stripe may be extruded onto the outer ~urface of at least one sidewall of the bag body. Further, the write-on film composition may be coextruded or formed as a blown multilayer film with the bag film composition. The result of coextrusion or a multilayer blown film results in efficient use of materials and results in thermal fusion, i.e., bonding, of the bag film and the write-on film composition. It has been observed (discussed in greater detail in reference to FIG. 38) that the coextrusion of the bag film and the write-on film stripe results in a thin layer of the bag film underlying the write-on film in the final multi-layered film. FIG. 38 shows a cross section of a bag film 60 and write-on film 58 formed by coextrusion. The coextrusion results in a thin layer of bag film 62 ad~acent the t~icker layer 58 of the write-on film.
The write-on film compositions of the instant invention are ~urface treated to provide the final write-on ~urface upon which a user will write for identification of some feature associated with use of the write-on surface. The ~ost commonly employed surface treatment is corona-discharge treatment. The use of corona-discharge treatment to ~odify the surface of a thermoplastic material to improve its write-on characteristic~ iB disclo~ed in U.S. Patent Nos. 2,810,933; 2,844,731; 4,051,044; and 4,710,358.
, Corona discharqe treaters are commercially available from numerous equipment manufacturers. Pillar Corporation, 475 Industrial Drive, Hartland, Wisconsin 53029, offer~ a line of corona treating power 6upplies in several wattages useful for corona-discharge treating thermoplastic materials.
In one embodiment the write-on 6urface i~ present on the outer ~urface of a bag sidewall and is corona-discharge treated at between about 50 and 150 watts/in2, preferably between about 100 and about 150 watts/in , using an arc-shaped treater approximately 1/16 inch from ~ silicon sleeved roller.
The write-on compositions of the instant invention have been described with respect to the first polymer and second polymer components and, optionally, the particulate material. The write-on composition may also contain commonly employed "additive" components as heretofore employed for the manufacture of polymer compositions. For example, it is within the scope of the instant write-on compositions to use various polymer additives, includinq, but not limited to, dyes, pigments, colorants, fillers, fluoroelastomers, ~tarch and cellulosic components, crosslinking agents, and mixtures thereof. It has been observed that the addition of starch to the write-on composition may further enhance the write-on characteri~tic~ of the write-on surface. AB well known in the art, ~uch additive component~ may typically be employed in an amount up to about 20 percent by weight or more of the overall weight of the write-on composition. It i~ preferred that the write-on composition contain no added 61ip agent, l.e., be sans ~lip agent, or contain the minimum amount required to carry out the manufacturing proces~ wherein the write-on composition is proceCce~, e.g., extruded or blown as a film. As will be readily apparent to one skilled in the art of extruding or blowing film products, the use of a slip agent may be required in some instances to effectively manufacture film products.
In one embodiment the write-on composition is provided as the component of a bag, preferably comprising a bag body having a reclosable feature, e.g., an adhesive or interlocking closure device attached thereto. In general, the bag may be any of those disclosed heretofore in the prior art and includes bags having features such as gussets, drawstrings, handles and the like. When the write-on composition of the instant invention is employed to provide a write-on area on the outer surface of the sidewall, any of the well known manufacturing processes for manufacturing the bag may be employed.
The bag body may be coextruded with a write-on stripe formed from the write-on compositions of the instant invention.
The instant invention also relates to a stack of bags comprising a plurality of bags, said bags having a write-on surface on a first bag sidewall and stacked in an alternating contacting manner such that said write-on surface on a first sidewall contacts a surface on a second sidewall having a slip agent therein, wherein the write-on surface comprises a corona-discharge treated, embossed write-on film wherein the write-on surface comprises:
a) a physical mixture of two substantially incompatible polymers wherein said second polymer is substantially incompatible in said first polymer; and b) a first particulate material comprising a particulate calcium carbonate in an effective amount to improve the writability of the corona-discharge treated write-on surface in contact with the slip 2030~67 agent-containing 6cc-on~ sidewall. In a further embodiment the invention relates to a stack of bags as aforementioned, comprising a corona-discharge treated write-on film surface wherein the film comprises:
a) a physical mixture of two substantially immiscible polymer~ wherein caid recon~ polymer is present in a minor amount and is a polyisobutylene and said first polymer is present in a major amount and is a low density polyethylene; and b) a particulate calcium carbonate material in an effective amount to improve the writability of said write-on film surface.
~XPERIMENTAL PROCEDURE
The film samples shown in FIG. 1 to FIG. 36 and discussed in Examples 1 to 16, inclusive, and as discussed hereinafter were prepared by coextruding a multilayer film comprising a low density polyethylene bag film comprising a low density polyethylene containing 1550 ppm of a slip agent (ecurimide) with a write-on film composition, as described in the DESCRIPTION OF THE DRAWINGS and in following examples, whereby a two layer film structure was formed, as shown in FIG. 38.
The write-on compositions of the instant invention were prepared by mixing the major resin component (low density polyethylene) into a container with the remaining components added thereafter by physical blending. The combined components were physically mixed until a homogeneous blend was observed. An extruded bag film was formed with a coextruded write-on composition as a write-on film stripe (as a 1.0 inch wide write-on stripe).
Referring to FIG. 37 and FIG. 38, the two layer film portion formed by the coextruded write-on film - 2030~67 and bag film had a total thickness of about 2.8 mil.
The bag film on either side of the two layer write-on film/bag film had a film thickness of about 2.5 mils. The thickness of the layer of coextruded bag film physically adjacent and in contact with the write-on film layer was about 2.1 mil. and the thickn~ss of the write-on film was about 0.7 mil.
Where indicated hereinafter, the write-on film compositions were prepared using masterbatch components as follows:
MASTERBATCH NO. 1 5 weight percent eurcimide in a low density polyethylene carrier polymer.
-MASTERBATCH NO. 270 weight percent TiO2 and in a low density polyethylene carrier polymer.
MASTERBATCH NO. 3 10 weight percent SYLOID~ silica in a low density polyethylene carrier polymer.
MASTERBATCH NO. 4 50 weight percent calcium carbonate in a low density polyethylene carrier polymer.
The film samples were prepared for the photomi~LGyLaph by the stAn~Ard gold sputtering method used for S.E.M. of dielectric materials. A
photomi~toyLaph of each sample was taken at magnifications of two hundred (200 X) and two thousand (2000 X).
The samples in each example were also provided with an embossed roll surface characterized as a grit-blasted matte surface available from PAMARACO, - 203~8~7 Inc. Roselle, New Jersey as pattern PAMA 14.
The write-on film curfaces were then tested for their writability by writing on each sample with a medium point ballpoint pen.
EXAMPLE 1 (FIG. 1 and FIG. 2):
This sample is a control sample containing 3000 ppm of the 81ip agent ecurimide and 4.5 weight percent Masterbatch No. 2 with the remainder comprising a low density polyethylene. The film sample was not surface treated by corona-~i~chArge.
Flat slip agent crystals are shown in this photograph as "A". The indentations ~hown as "B" on FIG. 1 represent the embossed pattern formed by use of the roll having the PAMA 14 pattern. The area designated by "C" demonstrates that the ink is not wetting the untreated film surface. FIG. 2 shows a 2000 X
magnification of area "C" of FIG. l further showing that the untreated film is not wet by the ink. In addition, FIG. 2 evidences the presence at the film surface of TiO2 particles which are designated as "D".
EXAMPLE 2 ~FIG. 3 and FIG. 4):
The film sample shown in FIGS. 3 and 4 is identical to that shown in FIG. 1, except the sample was corona-discharge ~urface treated at about 63.8 watts per ~quare inch. FIG. 3 and FIG. 4 show the effect the corona-discharge treating has on the slip agent crystals on the film ~urface. FIG. 3 ~hows that the ink is now wetting the surface in the area between A and A'. Per the theory for corona-discharge treatment, it is believed that the corona-discharge surface treatment "burns off" slip agent on the surface at the time of treatment, since the melting point of the slip agent (ecurimide) is `- 2~30867 only about 90 degrees centigrade (C). However, it has observed herein that slip agent (shown as "B") will migrate to the film surface and that this migrating slip agent cannot be burned off by the initial corona-discharge treatment, since it is not on the film surface during the corona-~i~ch~rge treatment. This slip agent bleeds to the film surface after corona-dirchArge surface treatment as the film ages and as the film is subjected to varying temperature conditions.
FIG. 3 and FIG. 4 also show surface Tio2 particles "D" and embossed areas "C".
EXAMPLE 3 (FIG. 5 and FIG. 6):
This film sample is the same as shown in FIG. 1 and 2, except it contains no slip agent. The crystals identified in FIGS. 1, 2, 3 and 4 as slip agent are no longer observed, although embossed area "A" and TiO2 particles "B" are observed on the film surface. FIG. 5 and FIG. 6 demonstrate that the untreated film surface (no corona-discharge treatment) is not wet by the ink (shown at "C").
FIG. 5 and FIG. 6 demonstrate the reliable, visual identification of the slip agent in FIG. 1 and FIG.
2. As aforementioned, the slip agent crystals are evidenced by the flat crystalline structure of the slip agent (ecurimide) crystals.
EXAMPLE 4 r FIG. 7 and FIG. 8):
FIG. 7 and FIG. 8 show a write-on film, according to the invention containing 10 weight percent ~xxFT~R~ PA-30, 3000 ppm slip agent, 4.5 weight percent of white masterbatch 2, with the remainder of the write-on composition being low density polyethylene. The film was not corona-discharge surface treated.
- 203~867 Referring to FIG. 7 and FIG. 8, it is readily apparent that the untreated film surface is dramatically different than the film surfaces shown in FIGS. 1 to 6, in that the film surface of FIG. 7 is extremely rouqh with an increased number of bumps. The observed bumps are caused by the substantial incompatibility of the polyisobutylene compound in the LDPE (low density polyethylene) component of the overall write-on film composition.
Surprisingly, crystals of slip agent are not readily observed in FIG. 7 or FIG. 8, demonstrating that some modification of slip agent at the write-on film surface has resulted from addition of the substantially incompatable polyisobutylene to the low density polyethylene.
It is also observed that the ink (shown at "A"
of FIG. 7) does not readily wet the film's untreated surface. The addition of the polyisobutylene component (shown as "B" on FIG. 8) alone did not facilitate signigicant wetting of the untreated film by the ink. The observed increase in roughness resulting from the presence of the polyisobutylene-containing component may also aid the rolling of the ball point in a ball point pen over the write-on film surface, although FIG. 7 and FIG. 8 demonstrate that the film surface must still be treated, e.g., corona-discharge treated, to allow the ink to wet the write-on film surface, as further discussed hereinafter in reference to FIG. 9 and FIG.
10 .
EXAMPLE 5 (FIG. 9 and FIG. 10~:
The write-on film ~ample shown in FIG. 9 and FIG. 10 is the same as the film sample shown in FIG.
7 and FIG. 8 , but the film has been corona-discharge treated at about 63.8 watts per square inch.
As shown in FIG. 9 and FIG. 10 the ink (between A and A' on FIG. 9 and between B and B' on FIG. 10) has wet the write-on film surface. Further, the polyisobutylene particles (shown as "C") have not been observed to have been affected by the corona-discharge treatment.
EXAMPLE 6 rFIG. 11 and FIG. 12):
A comparative film sample is shown in FIG. 11 and FIG. 12 containing a 4.5 wt. % Masterbatch No. 2, 10 wt. % SYLOID~ Masterbatch No. 3, and 3000 ppm slip agent (ecuramide) with the remainder being a low density polyethylene. The film sample was corona-discharge treated at 44.7 watts per squqre inch.
The corona-discharge treatment resulted in the ink (area between A and A') being able to wet the film surface. Although most of the particles seen at the film surface are the SYLOID~ silica particles "C", slip agent crystals "B" are observed at the film surface. It is readily observed that the film surface is not as rough as the film surface containing polyisobutylene, as shown in FIG. 9. Slip agent crystals are observed in FIG. 11 and FIG. 12 as flat crystal protrusions projecting from the film surface.
EXAMPLE 7 rFIG. 13 and FIG. 14):
A comparative film sample shown in FIG. 13 and FIG. 14 was prepared cont~ini~g 10 wt. % of SYLOID~
silica Masterbatch No. 3 and 4.5 wt. ~ Masterbatch No. 2 with the remainder being a LDPE. The film sample was corona-discharge treated at about 44.7 watts per square inch. FIG. 13 demonstrates that this sample has a high concentration of slip agent crystals on corona-discharge treated surface. The - 2030~67 presence of slip agent crystals in FIG. 13 is not surprising, since the film surface is abutted on three of it's four sides by a bag film containing a high concentration of Clip agent. The observation of slip agent crystals in FIG. 13 and FIG. 14 is to be contrasted with the write-on film surface according to the instant invention, containing the polyisobutylene component as di~Cllc~ above in Examples 4 and 5. Further, the film was wet by ink between A and A' of FIG. 13 and between B and B' of FIG. 14.
EXAMPLE 8 (FIG. 15 and FIG. 16):
A write-on film sample according to the instant invention is shown in FIG. 15 and FIG. 16 was formed containing 10 wt. % ~xx~TOR~ PA-30, 10 wt. %
Masterbatch No. 3, 4.5 wt. % Masterbatch No. 2 with the remainder of the write-on composition being a low density polyethylene. The write-on film was not corona-discharge surface treated. FIG. 15 and FIG.
16 demonstrate that the untreated film surface was not readily wet by the ink at "A". This should be compared to FIG. 7 chowing that Fxx~T~R~ PA-30 component alone with no corona-discharge treatment also did not aid in ink wetting of the film surface.
This film sample demonstrates that use of both ~xx~T~R~ PA-30 and the SYLOIDs~ silica (shown at "C" in FIG. 15) did not aid in the wetting the untreated film curface by the ink. Further, Tio2 particles are shown at "B" of FIG. 16 and the embossed pattern indentations are shown at "D" of FIG. 15.
EXAMPLE 9 (FIG. 17 ~nd FIG. 18~:
A write-on film sample, according to the instant invention, is shown in FIG. 17 and FIG. 18 and - 203~8~7 contains 10 wt % ~Xx~T~R~ PA-30, lO00 ppm slip agent (ecurimide), 5000 ppm of a diatomaceous earth, 4 . 5 wt. % Masterbatch No. 2 with the remainder of the write-on composition being a low density polyethylene. The film sample was corona-discharge treated at about 44 . 7 watts per square inch and aged at room temperature, i.e., about 2 5 - C . Although it has been observed that the SYLOIDs~ help prevent deterioration in the writability of an aged write-on film sample, similar testing of the sample of FIGS.
17 and 18 showed the natural diatomaceous earth (silica-containing) samples did not provide such a beneficial effect.
EXAMPLE 10 (FIG. 19 and FIG. 20):
The write-on film sample, shown in FIG. 19 and FIG. 20 was corona-discharge treated at 44 . 7 watts per square inch. This sample is the same as the sample shown in FIG. 15 and FIG. 16, except the sample has been given a corona-discharge treatment.
FIG. 19 and FIG. 20 demonstrate the effect of the corona-discharge treatment on a film composition containing a polyisobutylene component (~Xx~ToR~
PA-30) and a SYLOID~ silica , in that the ink is observed to wet the corona-discharge treated film surface. Further, the two film samples shown in FIG.
15 and FIG. 19 are identical, except for the corona-discharge treatment. FIG. l9 demonstrates the presence of the polyisobutylene component at the film surface after corona-discharge treatment.
Ex~PLE 11 (FIG. 21 and FIG. 22):
The write-on film sample shown in FIG. 21 and FIG. 22 contains 10 wt % Masterbatch No. 3 and 15 wt % ~X~TOR~ PA-30 with the remainder being a low density polyethylene. The write-on film sample was room temperature (about 25-C) aged for 9o days after corona-discharge treatment at 51 watts per square inch.
Referring to FIG. 21, it is observed that this film sample exhibits the rough surface characteristic of the substantially incompatible polymer mixture of polyisobutylene and low density polyethylene.
Further, the SYLOID~ particulate ~ilica particles (particles having a cize of about three microns) are also observed at the film surface. Rounded particles are also observed in FIG. 21 and FIG. 22 and are believed to be polyisobutylene particles partially melted during extrusion of the write-on film which then solidified at the lower melting point of the low density polyethylene film matrix. The rougher, more irregular particles observed in FIG. 21 and FIG. 22 are the SYLOID~ silica particles. FIG. 22 shows the ink edge running from about the middle of the left edge (at point A) to the middle of the bottom edge (at point A').
EXAMPLE 12 (FIG. 23 and FIG. 24~:
FIG. 23 and FIG. 24 show a film sample which is the same as shown in FIG. 21 and FIG. 22, except the ~xxFT~R~ PA-30 component has been replaced with an equal amount of an ~xx~T~R~ PA-50 component.
Satisfactory write-on characteristics according to the instant invention are observed for the film sample of FIG. 23 and FIG. 24. FIG. 24 shows what appears to be "puckered" area at "A". It is believed that this "puckered" area is an area of polyisobutylene which when corona-discharge treated acts differently when provided in the different carrier polymer (high density polyethylene) of X~T~R~ PA-50.
2~3a~67 EXAMPLE 13 (FIG. 25 and FIG. 26):
FIG. 25 and FIG. 26 is a film sample having the sample composition as that shown in FIG. 21, except the film sample has been oven aged at 140 degrees F
for four weeks. A high concentration of crystals is observed at the depression formed by the ballpoint of the ink pen. These cry6tals are identified as slip agent crystals which have bled (i.e., migrated) to the film surface through cracks formed by the ballpoint pen. It has been observed that when a ballpoint pen is drawn across the corona-di~chArge treated surface that the pressure exerted downward by the writing operation causes cracks in the brittle oxidized surface layer on the film formed as a result of the corona-discharge treatment. The 61ip agent is then free to "bleed" outwardly through the cracks as the ballpoint of the pen is drawn across the film surface.
EXAMPLE 14 (FIG. 27 and FIG. 28):
FIG. 27 and FIG. 28 show the sample of FIG. 23 but having been oven aged at 140 dey e28 F for about four weeks.
EXAMPLE 15 (FIG. 29 to FIG. 36):
The write-on film samples shown in FIGS. 29, 30, 31, 32, 33, 34, 35 and 36 were prepared using the hereinafter designated weight percents of Fx~T4R~ PA-50, a calcium carbonate (OMYACARB
FT having a mean particle diameter of 1.8 microns) and a low density polyethylene resin which did not contain a slip agent component. A write-on film was coextruded with a bag film as described in the Experimental Procedure, above. The write-on film surface was corona-discharge treated at 95.7 watts/in2. The following samples were prepared 203~867 and evaluated:
~XX~T~R
SAMPLE PA-50(conc) CaCO3(conc) Shown in FIGS.
1 10 5 29 and 30 2 20 5 31 and 32 3 10 10 33 and 34 4 20 10 35 and 36 The samples were written upon with a medium point ballpoint pen and 200X and 2000X photomiclGy~aphs taken.
Referring to FIGS. 29 to 36, the photomi~o~aphs show irregularly-shaped particles which are identified as particles of calcium carbonate and more spherically-shaped particles which are identified as discrete particles of ~X~R~ PA-50. Although the ink of the ballpoint pen is observed to wet the write-on film surface for each sample, the wetting observed for Sample 4 was judged to have been the best, based upon the ability of the ink to wet the write-on film surface. An increase in the concentration of the calcium carbonate component to about 25`wt. % is believed to be advantageous.
EXAMPLE 16:
Samples of corona-discharge treated write-on film were made containing various amounts of ~Xx~T~R~ PA-50, CaCO3 and/or SYLOID~ silica, as set forth below, with the remainder comprising a low density polyethylene ("LDPE").
A paired comparison of the samples by five ~udges showed that when CaCO3 was incorporated as a particulate material that the film sample containing ~X~R~ PA-50 and CaCO3 was judged to improve the writability of the sample after aging (at a 90 percent confidence limit) over the other samples. The following film samples were prepared, embossed and corona-discharge treated according to the above-described Experimental 203gl867 Procedure:
~XX~T~R~ SYLOID
SAMPLE3 PA-50 CaCO31 Silica2 1 Added as 50 wt. % CaCO3 in a low density polyethylene.
2 Added as 50 wt. % silica in a low density polyethylene.
3 Corona-discharge treated at 95.8 watts/in2.
4,822,539; and 4,829,641.
When the closure bag is a color change closure bag as disclosed in U.S. Patent Nos.
4,363,345 and 4,829,641 it is preferred to provide the write-on ~urface on the 6idewall of the bag having the translucent closure element, although such is not required. By providing the write-on ~urface on the sidewall having tbe translucent closure element the user of the closure bag can first close the baq while observing the color change of the color change closure and then write on the wrlte-on surface without the necessity of turning over the bag to access the write-on 6urface. ~he embodiment wherein a write-on 6tripe i6 provided on a sidewall of a closure-ty~pe bag i6 ~hown in FIG. 37. FIG. 37 ~hows a typical flexible container 40 formed from a thin plastic film which bas been folded to define a bottom portion 41 and heat 6ealed along vertical edges 42 to form a pouch. The 6idewall6 43 extend beyond a closure device (optional) compri~ed of closure -203~867 elements 50 and 52 to provide flanges 45 and mouth portions 46 and 48 to simplify the opening and closing of closure elements 50 and 52. A write-on stripe surface 46 is provided according to the instant invention.
The term "film", as used herein and in the prior art, represents any three-dimensional material which pos~es~^s two opposite facing surfaces separated by edging surfaces. The opposite facing surfaces may be mono- or poly-planar and the combined surfaces typically (and preferably) poscess many times the area of the edge surfaces. The film, e.g., bag film, which may be employed with a write-on surface in the practice of the invention may be any film, including plastic, resin, metal, textile, fiber reinforced plastic or resin, ceramic, glass, rubber, paper and cardboard, wallboard, composites thereof, and the like to which the write-on film may be associated, e.g., affixed. The composite films may be employed to make bag structures. The films employed in the manufacture of bags are typically polyolefin thermoplastic films such as one or more layers of one or more of polyethylene (low density, high density, linear low density, ultra low density and/or combinations thereof), polypropylene, polyethylene copolymers (low density, linear low density, ultra low density, high density and/or combinations), polybutylenes, ABS polymers, polyurethanes, polycarbonates, polysulphones, aliphatic polyamides, polyarylamides, polyaryletherketones, polyarylimideamides, polyaryletherimides, polyesters, polyarylates, polyoxymethylene, poly(epsilon-caprolactone), and the like, alone or composited with a variety of materials, such as metal films, paper, cardboard, textile structures, wood, and the like.
2030~67 The write-on compositions of the instant inventions are preferably employed as films and may be extruded or blown, preferably extruded, using conventional manufacturing processes and parameters.
For example, the instant write-on compositions may be employed as an extruded write-on stripe on a thermoplastic film, e.g., a 0.5 to 1 inch wide stripe. When the film is employed to form a bag the stripe may be extruded onto the outer ~urface of at least one sidewall of the bag body. Further, the write-on film composition may be coextruded or formed as a blown multilayer film with the bag film composition. The result of coextrusion or a multilayer blown film results in efficient use of materials and results in thermal fusion, i.e., bonding, of the bag film and the write-on film composition. It has been observed (discussed in greater detail in reference to FIG. 38) that the coextrusion of the bag film and the write-on film stripe results in a thin layer of the bag film underlying the write-on film in the final multi-layered film. FIG. 38 shows a cross section of a bag film 60 and write-on film 58 formed by coextrusion. The coextrusion results in a thin layer of bag film 62 ad~acent the t~icker layer 58 of the write-on film.
The write-on film compositions of the instant invention are ~urface treated to provide the final write-on ~urface upon which a user will write for identification of some feature associated with use of the write-on surface. The ~ost commonly employed surface treatment is corona-discharge treatment. The use of corona-discharge treatment to ~odify the surface of a thermoplastic material to improve its write-on characteristic~ iB disclo~ed in U.S. Patent Nos. 2,810,933; 2,844,731; 4,051,044; and 4,710,358.
, Corona discharqe treaters are commercially available from numerous equipment manufacturers. Pillar Corporation, 475 Industrial Drive, Hartland, Wisconsin 53029, offer~ a line of corona treating power 6upplies in several wattages useful for corona-discharge treating thermoplastic materials.
In one embodiment the write-on 6urface i~ present on the outer ~urface of a bag sidewall and is corona-discharge treated at between about 50 and 150 watts/in2, preferably between about 100 and about 150 watts/in , using an arc-shaped treater approximately 1/16 inch from ~ silicon sleeved roller.
The write-on compositions of the instant invention have been described with respect to the first polymer and second polymer components and, optionally, the particulate material. The write-on composition may also contain commonly employed "additive" components as heretofore employed for the manufacture of polymer compositions. For example, it is within the scope of the instant write-on compositions to use various polymer additives, includinq, but not limited to, dyes, pigments, colorants, fillers, fluoroelastomers, ~tarch and cellulosic components, crosslinking agents, and mixtures thereof. It has been observed that the addition of starch to the write-on composition may further enhance the write-on characteri~tic~ of the write-on surface. AB well known in the art, ~uch additive component~ may typically be employed in an amount up to about 20 percent by weight or more of the overall weight of the write-on composition. It i~ preferred that the write-on composition contain no added 61ip agent, l.e., be sans ~lip agent, or contain the minimum amount required to carry out the manufacturing proces~ wherein the write-on composition is proceCce~, e.g., extruded or blown as a film. As will be readily apparent to one skilled in the art of extruding or blowing film products, the use of a slip agent may be required in some instances to effectively manufacture film products.
In one embodiment the write-on composition is provided as the component of a bag, preferably comprising a bag body having a reclosable feature, e.g., an adhesive or interlocking closure device attached thereto. In general, the bag may be any of those disclosed heretofore in the prior art and includes bags having features such as gussets, drawstrings, handles and the like. When the write-on composition of the instant invention is employed to provide a write-on area on the outer surface of the sidewall, any of the well known manufacturing processes for manufacturing the bag may be employed.
The bag body may be coextruded with a write-on stripe formed from the write-on compositions of the instant invention.
The instant invention also relates to a stack of bags comprising a plurality of bags, said bags having a write-on surface on a first bag sidewall and stacked in an alternating contacting manner such that said write-on surface on a first sidewall contacts a surface on a second sidewall having a slip agent therein, wherein the write-on surface comprises a corona-discharge treated, embossed write-on film wherein the write-on surface comprises:
a) a physical mixture of two substantially incompatible polymers wherein said second polymer is substantially incompatible in said first polymer; and b) a first particulate material comprising a particulate calcium carbonate in an effective amount to improve the writability of the corona-discharge treated write-on surface in contact with the slip 2030~67 agent-containing 6cc-on~ sidewall. In a further embodiment the invention relates to a stack of bags as aforementioned, comprising a corona-discharge treated write-on film surface wherein the film comprises:
a) a physical mixture of two substantially immiscible polymer~ wherein caid recon~ polymer is present in a minor amount and is a polyisobutylene and said first polymer is present in a major amount and is a low density polyethylene; and b) a particulate calcium carbonate material in an effective amount to improve the writability of said write-on film surface.
~XPERIMENTAL PROCEDURE
The film samples shown in FIG. 1 to FIG. 36 and discussed in Examples 1 to 16, inclusive, and as discussed hereinafter were prepared by coextruding a multilayer film comprising a low density polyethylene bag film comprising a low density polyethylene containing 1550 ppm of a slip agent (ecurimide) with a write-on film composition, as described in the DESCRIPTION OF THE DRAWINGS and in following examples, whereby a two layer film structure was formed, as shown in FIG. 38.
The write-on compositions of the instant invention were prepared by mixing the major resin component (low density polyethylene) into a container with the remaining components added thereafter by physical blending. The combined components were physically mixed until a homogeneous blend was observed. An extruded bag film was formed with a coextruded write-on composition as a write-on film stripe (as a 1.0 inch wide write-on stripe).
Referring to FIG. 37 and FIG. 38, the two layer film portion formed by the coextruded write-on film - 2030~67 and bag film had a total thickness of about 2.8 mil.
The bag film on either side of the two layer write-on film/bag film had a film thickness of about 2.5 mils. The thickness of the layer of coextruded bag film physically adjacent and in contact with the write-on film layer was about 2.1 mil. and the thickn~ss of the write-on film was about 0.7 mil.
Where indicated hereinafter, the write-on film compositions were prepared using masterbatch components as follows:
MASTERBATCH NO. 1 5 weight percent eurcimide in a low density polyethylene carrier polymer.
-MASTERBATCH NO. 270 weight percent TiO2 and in a low density polyethylene carrier polymer.
MASTERBATCH NO. 3 10 weight percent SYLOID~ silica in a low density polyethylene carrier polymer.
MASTERBATCH NO. 4 50 weight percent calcium carbonate in a low density polyethylene carrier polymer.
The film samples were prepared for the photomi~LGyLaph by the stAn~Ard gold sputtering method used for S.E.M. of dielectric materials. A
photomi~toyLaph of each sample was taken at magnifications of two hundred (200 X) and two thousand (2000 X).
The samples in each example were also provided with an embossed roll surface characterized as a grit-blasted matte surface available from PAMARACO, - 203~8~7 Inc. Roselle, New Jersey as pattern PAMA 14.
The write-on film curfaces were then tested for their writability by writing on each sample with a medium point ballpoint pen.
EXAMPLE 1 (FIG. 1 and FIG. 2):
This sample is a control sample containing 3000 ppm of the 81ip agent ecurimide and 4.5 weight percent Masterbatch No. 2 with the remainder comprising a low density polyethylene. The film sample was not surface treated by corona-~i~chArge.
Flat slip agent crystals are shown in this photograph as "A". The indentations ~hown as "B" on FIG. 1 represent the embossed pattern formed by use of the roll having the PAMA 14 pattern. The area designated by "C" demonstrates that the ink is not wetting the untreated film surface. FIG. 2 shows a 2000 X
magnification of area "C" of FIG. l further showing that the untreated film is not wet by the ink. In addition, FIG. 2 evidences the presence at the film surface of TiO2 particles which are designated as "D".
EXAMPLE 2 ~FIG. 3 and FIG. 4):
The film sample shown in FIGS. 3 and 4 is identical to that shown in FIG. 1, except the sample was corona-discharge ~urface treated at about 63.8 watts per ~quare inch. FIG. 3 and FIG. 4 show the effect the corona-discharge treating has on the slip agent crystals on the film ~urface. FIG. 3 ~hows that the ink is now wetting the surface in the area between A and A'. Per the theory for corona-discharge treatment, it is believed that the corona-discharge surface treatment "burns off" slip agent on the surface at the time of treatment, since the melting point of the slip agent (ecurimide) is `- 2~30867 only about 90 degrees centigrade (C). However, it has observed herein that slip agent (shown as "B") will migrate to the film surface and that this migrating slip agent cannot be burned off by the initial corona-discharge treatment, since it is not on the film surface during the corona-~i~ch~rge treatment. This slip agent bleeds to the film surface after corona-dirchArge surface treatment as the film ages and as the film is subjected to varying temperature conditions.
FIG. 3 and FIG. 4 also show surface Tio2 particles "D" and embossed areas "C".
EXAMPLE 3 (FIG. 5 and FIG. 6):
This film sample is the same as shown in FIG. 1 and 2, except it contains no slip agent. The crystals identified in FIGS. 1, 2, 3 and 4 as slip agent are no longer observed, although embossed area "A" and TiO2 particles "B" are observed on the film surface. FIG. 5 and FIG. 6 demonstrate that the untreated film surface (no corona-discharge treatment) is not wet by the ink (shown at "C").
FIG. 5 and FIG. 6 demonstrate the reliable, visual identification of the slip agent in FIG. 1 and FIG.
2. As aforementioned, the slip agent crystals are evidenced by the flat crystalline structure of the slip agent (ecurimide) crystals.
EXAMPLE 4 r FIG. 7 and FIG. 8):
FIG. 7 and FIG. 8 show a write-on film, according to the invention containing 10 weight percent ~xxFT~R~ PA-30, 3000 ppm slip agent, 4.5 weight percent of white masterbatch 2, with the remainder of the write-on composition being low density polyethylene. The film was not corona-discharge surface treated.
- 203~867 Referring to FIG. 7 and FIG. 8, it is readily apparent that the untreated film surface is dramatically different than the film surfaces shown in FIGS. 1 to 6, in that the film surface of FIG. 7 is extremely rouqh with an increased number of bumps. The observed bumps are caused by the substantial incompatibility of the polyisobutylene compound in the LDPE (low density polyethylene) component of the overall write-on film composition.
Surprisingly, crystals of slip agent are not readily observed in FIG. 7 or FIG. 8, demonstrating that some modification of slip agent at the write-on film surface has resulted from addition of the substantially incompatable polyisobutylene to the low density polyethylene.
It is also observed that the ink (shown at "A"
of FIG. 7) does not readily wet the film's untreated surface. The addition of the polyisobutylene component (shown as "B" on FIG. 8) alone did not facilitate signigicant wetting of the untreated film by the ink. The observed increase in roughness resulting from the presence of the polyisobutylene-containing component may also aid the rolling of the ball point in a ball point pen over the write-on film surface, although FIG. 7 and FIG. 8 demonstrate that the film surface must still be treated, e.g., corona-discharge treated, to allow the ink to wet the write-on film surface, as further discussed hereinafter in reference to FIG. 9 and FIG.
10 .
EXAMPLE 5 (FIG. 9 and FIG. 10~:
The write-on film ~ample shown in FIG. 9 and FIG. 10 is the same as the film sample shown in FIG.
7 and FIG. 8 , but the film has been corona-discharge treated at about 63.8 watts per square inch.
As shown in FIG. 9 and FIG. 10 the ink (between A and A' on FIG. 9 and between B and B' on FIG. 10) has wet the write-on film surface. Further, the polyisobutylene particles (shown as "C") have not been observed to have been affected by the corona-discharge treatment.
EXAMPLE 6 rFIG. 11 and FIG. 12):
A comparative film sample is shown in FIG. 11 and FIG. 12 containing a 4.5 wt. % Masterbatch No. 2, 10 wt. % SYLOID~ Masterbatch No. 3, and 3000 ppm slip agent (ecuramide) with the remainder being a low density polyethylene. The film sample was corona-discharge treated at 44.7 watts per squqre inch.
The corona-discharge treatment resulted in the ink (area between A and A') being able to wet the film surface. Although most of the particles seen at the film surface are the SYLOID~ silica particles "C", slip agent crystals "B" are observed at the film surface. It is readily observed that the film surface is not as rough as the film surface containing polyisobutylene, as shown in FIG. 9. Slip agent crystals are observed in FIG. 11 and FIG. 12 as flat crystal protrusions projecting from the film surface.
EXAMPLE 7 rFIG. 13 and FIG. 14):
A comparative film sample shown in FIG. 13 and FIG. 14 was prepared cont~ini~g 10 wt. % of SYLOID~
silica Masterbatch No. 3 and 4.5 wt. ~ Masterbatch No. 2 with the remainder being a LDPE. The film sample was corona-discharge treated at about 44.7 watts per square inch. FIG. 13 demonstrates that this sample has a high concentration of slip agent crystals on corona-discharge treated surface. The - 2030~67 presence of slip agent crystals in FIG. 13 is not surprising, since the film surface is abutted on three of it's four sides by a bag film containing a high concentration of Clip agent. The observation of slip agent crystals in FIG. 13 and FIG. 14 is to be contrasted with the write-on film surface according to the instant invention, containing the polyisobutylene component as di~Cllc~ above in Examples 4 and 5. Further, the film was wet by ink between A and A' of FIG. 13 and between B and B' of FIG. 14.
EXAMPLE 8 (FIG. 15 and FIG. 16):
A write-on film sample according to the instant invention is shown in FIG. 15 and FIG. 16 was formed containing 10 wt. % ~xx~TOR~ PA-30, 10 wt. %
Masterbatch No. 3, 4.5 wt. % Masterbatch No. 2 with the remainder of the write-on composition being a low density polyethylene. The write-on film was not corona-discharge surface treated. FIG. 15 and FIG.
16 demonstrate that the untreated film surface was not readily wet by the ink at "A". This should be compared to FIG. 7 chowing that Fxx~T~R~ PA-30 component alone with no corona-discharge treatment also did not aid in ink wetting of the film surface.
This film sample demonstrates that use of both ~xx~T~R~ PA-30 and the SYLOIDs~ silica (shown at "C" in FIG. 15) did not aid in the wetting the untreated film curface by the ink. Further, Tio2 particles are shown at "B" of FIG. 16 and the embossed pattern indentations are shown at "D" of FIG. 15.
EXAMPLE 9 (FIG. 17 ~nd FIG. 18~:
A write-on film sample, according to the instant invention, is shown in FIG. 17 and FIG. 18 and - 203~8~7 contains 10 wt % ~Xx~T~R~ PA-30, lO00 ppm slip agent (ecurimide), 5000 ppm of a diatomaceous earth, 4 . 5 wt. % Masterbatch No. 2 with the remainder of the write-on composition being a low density polyethylene. The film sample was corona-discharge treated at about 44 . 7 watts per square inch and aged at room temperature, i.e., about 2 5 - C . Although it has been observed that the SYLOIDs~ help prevent deterioration in the writability of an aged write-on film sample, similar testing of the sample of FIGS.
17 and 18 showed the natural diatomaceous earth (silica-containing) samples did not provide such a beneficial effect.
EXAMPLE 10 (FIG. 19 and FIG. 20):
The write-on film sample, shown in FIG. 19 and FIG. 20 was corona-discharge treated at 44 . 7 watts per square inch. This sample is the same as the sample shown in FIG. 15 and FIG. 16, except the sample has been given a corona-discharge treatment.
FIG. 19 and FIG. 20 demonstrate the effect of the corona-discharge treatment on a film composition containing a polyisobutylene component (~Xx~ToR~
PA-30) and a SYLOID~ silica , in that the ink is observed to wet the corona-discharge treated film surface. Further, the two film samples shown in FIG.
15 and FIG. 19 are identical, except for the corona-discharge treatment. FIG. l9 demonstrates the presence of the polyisobutylene component at the film surface after corona-discharge treatment.
Ex~PLE 11 (FIG. 21 and FIG. 22):
The write-on film sample shown in FIG. 21 and FIG. 22 contains 10 wt % Masterbatch No. 3 and 15 wt % ~X~TOR~ PA-30 with the remainder being a low density polyethylene. The write-on film sample was room temperature (about 25-C) aged for 9o days after corona-discharge treatment at 51 watts per square inch.
Referring to FIG. 21, it is observed that this film sample exhibits the rough surface characteristic of the substantially incompatible polymer mixture of polyisobutylene and low density polyethylene.
Further, the SYLOID~ particulate ~ilica particles (particles having a cize of about three microns) are also observed at the film surface. Rounded particles are also observed in FIG. 21 and FIG. 22 and are believed to be polyisobutylene particles partially melted during extrusion of the write-on film which then solidified at the lower melting point of the low density polyethylene film matrix. The rougher, more irregular particles observed in FIG. 21 and FIG. 22 are the SYLOID~ silica particles. FIG. 22 shows the ink edge running from about the middle of the left edge (at point A) to the middle of the bottom edge (at point A').
EXAMPLE 12 (FIG. 23 and FIG. 24~:
FIG. 23 and FIG. 24 show a film sample which is the same as shown in FIG. 21 and FIG. 22, except the ~xxFT~R~ PA-30 component has been replaced with an equal amount of an ~xx~T~R~ PA-50 component.
Satisfactory write-on characteristics according to the instant invention are observed for the film sample of FIG. 23 and FIG. 24. FIG. 24 shows what appears to be "puckered" area at "A". It is believed that this "puckered" area is an area of polyisobutylene which when corona-discharge treated acts differently when provided in the different carrier polymer (high density polyethylene) of X~T~R~ PA-50.
2~3a~67 EXAMPLE 13 (FIG. 25 and FIG. 26):
FIG. 25 and FIG. 26 is a film sample having the sample composition as that shown in FIG. 21, except the film sample has been oven aged at 140 degrees F
for four weeks. A high concentration of crystals is observed at the depression formed by the ballpoint of the ink pen. These cry6tals are identified as slip agent crystals which have bled (i.e., migrated) to the film surface through cracks formed by the ballpoint pen. It has been observed that when a ballpoint pen is drawn across the corona-di~chArge treated surface that the pressure exerted downward by the writing operation causes cracks in the brittle oxidized surface layer on the film formed as a result of the corona-discharge treatment. The 61ip agent is then free to "bleed" outwardly through the cracks as the ballpoint of the pen is drawn across the film surface.
EXAMPLE 14 (FIG. 27 and FIG. 28):
FIG. 27 and FIG. 28 show the sample of FIG. 23 but having been oven aged at 140 dey e28 F for about four weeks.
EXAMPLE 15 (FIG. 29 to FIG. 36):
The write-on film samples shown in FIGS. 29, 30, 31, 32, 33, 34, 35 and 36 were prepared using the hereinafter designated weight percents of Fx~T4R~ PA-50, a calcium carbonate (OMYACARB
FT having a mean particle diameter of 1.8 microns) and a low density polyethylene resin which did not contain a slip agent component. A write-on film was coextruded with a bag film as described in the Experimental Procedure, above. The write-on film surface was corona-discharge treated at 95.7 watts/in2. The following samples were prepared 203~867 and evaluated:
~XX~T~R
SAMPLE PA-50(conc) CaCO3(conc) Shown in FIGS.
1 10 5 29 and 30 2 20 5 31 and 32 3 10 10 33 and 34 4 20 10 35 and 36 The samples were written upon with a medium point ballpoint pen and 200X and 2000X photomiclGy~aphs taken.
Referring to FIGS. 29 to 36, the photomi~o~aphs show irregularly-shaped particles which are identified as particles of calcium carbonate and more spherically-shaped particles which are identified as discrete particles of ~X~R~ PA-50. Although the ink of the ballpoint pen is observed to wet the write-on film surface for each sample, the wetting observed for Sample 4 was judged to have been the best, based upon the ability of the ink to wet the write-on film surface. An increase in the concentration of the calcium carbonate component to about 25`wt. % is believed to be advantageous.
EXAMPLE 16:
Samples of corona-discharge treated write-on film were made containing various amounts of ~Xx~T~R~ PA-50, CaCO3 and/or SYLOID~ silica, as set forth below, with the remainder comprising a low density polyethylene ("LDPE").
A paired comparison of the samples by five ~udges showed that when CaCO3 was incorporated as a particulate material that the film sample containing ~X~R~ PA-50 and CaCO3 was judged to improve the writability of the sample after aging (at a 90 percent confidence limit) over the other samples. The following film samples were prepared, embossed and corona-discharge treated according to the above-described Experimental 203gl867 Procedure:
~XX~T~R~ SYLOID
SAMPLE3 PA-50 CaCO31 Silica2 1 Added as 50 wt. % CaCO3 in a low density polyethylene.
2 Added as 50 wt. % silica in a low density polyethylene.
3 Corona-discharge treated at 95.8 watts/in2.
Claims (56)
1. A bag having a write-on film surface comprising a slip agent containing bag film for forming a bag body and a write-on film contacting said bag film wherein said write-on film surface comprises an effectively surface treated write-on film wherein the write-on film comprises a physical mixture, sans slip agent, of two substantially incompatible polymers, wherein a second polymer is substantially incompatible in a first polymer and an effective amount of a calcium carbonate as a first particulate material, wherein the weight ratio of said first polymer to said second polymer is between about 10:1 and about 1:10.
2. A bag according to claim 1 wherein said bag film is a low density polyethylene film and said write-on film surface comprises low density polyethylene as said first polymer and polyisobutylene as said second polymer.
3. A bag according to claim 1 wherein said bag film is a low density polyethylene film and said write-on film comprises polypropylene as said first polymer and polyisobutylene as said second polymer.
4. A bag according to claim 1 wherein the weight ratio of the thickness of bag film to the thickness of said contacting write-on film is between about 1:2 and about 1:10.
5. A bag according to claim 1 or claim 2 wherein the slip agent in said bag film is a C18 to C22 fatty acid amide and is present in an amount between about 500 ppm and about 2500 ppm.
6. A bag according to claim 5 wherein the slip agent is present in an amount between about 1000 ppm and about 2000 ppm.
7. A bag according to claim 1 wherein said write-on film is embossed.
8. A bag according to claim 1 or claim 2 or claim 3 wherein said write-on film additionally comprises a second particulate material present.
9. A bag according to claim 8 wherein said write-on film comprises a particulate material present in an effective amount to improve the writability of said write-on film when aged in the presence of slip agent.
10. A bag according to claim 9 wherein said silica is a silica having a surface area of about 350 m2/g, an average particle size of about 3.0 microns and a density of about 8 lbs/ft3.
11. A bag according to claim 1 wherein the thickness of the write-on film is greater than about 30 percent of the total thickness of the combined thickness of the write-on film and bag film where said write-on film contacts said bag film.
12. A bag according to claim 1 wherein said first particulate material is present in an effective amount between about 3.0 wt. % and about 20 wt. % to improve the writability of said write-on film surface when aged.
13. A bag according to claim 1 wherein said bag film comprises a low density polyethylene containing between about 500 ppm and about 2500 ppm slip agent and said write-on film is a mixture of a minor amount of the polymer component of polyisobutylene and a major amount of the polymer component of at least one polymer selected from the group consisting of polyethylene and polypropylene.
14. A bag according to claim 13 wherein said slip agent is ecurimide present in an amount between about 1000 ppm and about 0500 ppm and said particulate material is a mixture of a titanium dioxide and calcium carbonate present in an amount between about 3.0 wt. %
and about 20 wt. %.
and about 20 wt. %.
15. A bag according to claim 1 wherein said write-on surface is corona-discharge treated and wherein: (1) said bag film is a polyethylene having a density between about 0.915 and about 0.930 grams per cubic centimeter containing between about 500 ppm and about 2500 ppm of ecurimide as said slip agent; and (2) said write-on film comprises a major amount of at least one polymer selected from the group consisting of low density polyethylene, high density polyethylene and polypropylene, a minor amount of at least one polymer selected from the group consisting of EXXELOR# PA-30, EXXELOR# PA-50, with the proviso that said write-on film as formed is substantially without slip agent, between about 3.0 wt. % and about 20 wt. % of a calcium carbonate having a particle size distribution with about 50 percent of said particles less than 2 microns and about 30 percent of said particles less than 1 micron; and, (3) said write-on film is embossed.
16. A bag according to claim 1 or claim 2 or claim 3 or claim 15 wherein said corona-discharge treated at between about 50 watts/in2 and about 150 watts/in2.
17. A bag according to claim 1 or claim 15 wherein said bag is a closure-type bag.
18. A bag according to claim 17 wherein said closure bag is a color-change closure bag having a translucent closure element and an opaque closure element on respective bag sidewalls.
19. A bag according to claim 18 wherein said write-on film is on said sidewall of said closure bag having said translucent closure element.
20. A bag according to claim 1 or claim 15 comprising a corona-discharge treated write-on film in contact with said bag film wherein the write-on film has a thickness of about 2.1 mils and said contacting bag film has a thickness of about 0.7 mil.
21. A bag according to claim 20 wherein the write-on film and bag film are formed by coextrusion.
22. A write-on surface comprising a corona-discharge surface treated polymer composition comprising:
a) a physical mixture without slip agent of two polymers where a second polymer is substantially incompatible in a first polymer; and b) an effective amount of a calcium carbonate as a first particulate material, wherein the weight ratio of said first polymer-to said second polymer is between about 10:1 and about 1:10.
a) a physical mixture without slip agent of two polymers where a second polymer is substantially incompatible in a first polymer; and b) an effective amount of a calcium carbonate as a first particulate material, wherein the weight ratio of said first polymer-to said second polymer is between about 10:1 and about 1:10.
23. A write-on surface according to claim 22 comprising a corona-discharge treated write-on composition comprising:
a) polyisobutylene as said second polymer present in a minor amount of said first polymer component and said first polymer component present in a major amount of said polymer component is selected from the group consisting of low density polyethylene, high density polyethylene, polyvinyl alcohol, polypropylene, butadiene/styrene and mixtures thereof;
and b) a second particulate material selected from the group consisting of silica, titanium dioxide, talc, starch, and mixtures thereof.
a) polyisobutylene as said second polymer present in a minor amount of said first polymer component and said first polymer component present in a major amount of said polymer component is selected from the group consisting of low density polyethylene, high density polyethylene, polyvinyl alcohol, polypropylene, butadiene/styrene and mixtures thereof;
and b) a second particulate material selected from the group consisting of silica, titanium dioxide, talc, starch, and mixtures thereof.
24. A write-on surface according to claim 23 wherein said write-on composition comprises a major amount of a low density polyethylene and a minor amount of a polyisobutylene.
25. A write-on surface according to claim 23 wherein said write-on composition comprises a major amount of a polypropylene and a minor amount of a polyisobutylene.
26. A write-on composition according to claim 24 wherein the corona-discharge treatment is conducted at between about 50 watts/in2 and about 150 watts/in 2.
27. A write-on surface according to claim 23 wherein the corona-discharge treatment is conducted at between about 50 watts/in2 and about 100 watts/in2.
28. A write-on surface according to claim 22 wherein said write-on surface is embossed.
29. A write-on surface according to claim 23 or claim 26 wherein said write-on surface is embossed.
30. A write-on film comprising a corona-discharge treated, embossed without slip agent film composition comprising the following components:
(1) a polymer component comprising a major amount of a low density polyethylene and a minor amount of a polyisobutylene; and (2) an effective amount of a calcium carbonate as a particulate material.
(1) a polymer component comprising a major amount of a low density polyethylene and a minor amount of a polyisobutylene; and (2) an effective amount of a calcium carbonate as a particulate material.
31. A write-on film according to claim 30 wherein said particulate material additionally comprises a second particulate material selected from the group consisting of silica, titanium dioxide and mixtures thereof.
32. A write-on film according to claim 31 wherein said second particulate material is titanium dioxide.
33. A stack of bags comprising a plurality of bags, said bags having a write-on surface on a first bag sidewall and stacked in an alternating contacting manner such that said write-on surface on a first sidewall contacts a surface on a second sidewall having a slip agent therein, wherein the write-on surface comprises a corona-discharge treated, embossed write-on film wherein the write-on surface comprises:
a) a physical mixture of two substantially incompatible polymers wherein said second polymer is substantially incompatible in said first polymer; and b) a particulate material comprising a particulate calcium carbonate in an effective amount to improve the writability of the corona-discharge treated write-on surface in contact with the slip agent-containing second sidewall, wherein the weight ratio of said first polymer to said second polymer is between about 10:1 and about 1:10.
a) a physical mixture of two substantially incompatible polymers wherein said second polymer is substantially incompatible in said first polymer; and b) a particulate material comprising a particulate calcium carbonate in an effective amount to improve the writability of the corona-discharge treated write-on surface in contact with the slip agent-containing second sidewall, wherein the weight ratio of said first polymer to said second polymer is between about 10:1 and about 1:10.
34. A stack of bags according to claim 33 comprising a corona-discharge treated write-on film surface wherein the film comprises:
a) a physical mixture of two substantially immiscible polymers wherein said second polymer is present in a minor amount and is a polyisobutylene and said first polymer is present in a major amount and is a low density polyethylene; and b) a particulate calcium carbonate material in an effective amount to improve the writability of said write-on film surface.
a) a physical mixture of two substantially immiscible polymers wherein said second polymer is present in a minor amount and is a polyisobutylene and said first polymer is present in a major amount and is a low density polyethylene; and b) a particulate calcium carbonate material in an effective amount to improve the writability of said write-on film surface.
35. A stack of bags according to claim 33 wherein said bag film is a low density polyethylene film and said write-on film surface comprises low density polyethylene as said first polymer and polyisobutylene as said second polymer.
36. A stack of bags according to claim 33 wherein said bag film is a low density polyethylene film and said write-on film comprises polypropylene as said first polymer and polyisobutylene as said second polymer.
37. A stack of bags according to claim 33 wherein the weight ratio of said first polymer to said second polymer is between about 10:1 and about 1:10.
38. A stack of bags according to claim 33 or claim 34 wherein the slip agent in said bag film is ecurimide and is present in an amount between about 500 ppm and about 2500 ppm.
39. A stack of bags according to claim 38 wherein the slip agent is present in an amount between about 1000 ppm and about 2000 ppm.
40. A stack of bags according to claim 33 wherein said write-on film is embossed.
41. A stack of bags according to claim 33 or claim 34 wherein said write-on film additionally comprises a second particulate material present.
42. A stack of bags according to claim 33 wherein a write-on film comprises a particulate material present in an effective amount to improve the writability of said write-on film when aged in the presence of slip agent.
43. A stack of bags according to claim 42 wherein a second particulate material is present and is at least one particulate material selected from the group consisting of silica and titanium dioxide.
44. A stack of bags according to claim 43 wherein said silica is a silica having a surface area of about 350 m2/g, an average particle size of about 3.0 microns and a density of about 8 lbs/ft3.
45. A stack of bags according to claim 33 or claim 34 wherein the thickness of the write-on film is greater than about 30 percent of the total thickness of the combined thickness of the write-on film and bag film where said write-on film contacts said bag film.
46. A stack of bags according to claim 33 wherein said first particulate material is present in an effective amount between about 3.0 wt. % and about 20 wt. % to improve the writability of said write-on film surface when aged.
47. A stack of bags according to claim 37 wherein said bag film comprises a low density polyethylene containing between about 500 ppm and about 2500 ppm slip agent and said write-on film is a mixture of a minor amount of polyisobutylene and a major amount of at least one polymer selected from the group consisting of low density polyethylene and polypropylene.
48. A stack of bags according to claim 47 wherein said slip agent is ecurimide present in an amount between about 1000 ppm and about 0500 ppm and said particulate material is a mixture of a titanium dioxide and calcium carbonate present in an amount between about 3.0 wt. % and about 20 wt. %.
49. A stack of bags according to claim 33 wherein:
(1) said bag film is a low density polyethylene having a density between about 0.915 and about 0.930 grams per cubic centimeter containing between about 500 ppm and about 2500 ppm of ecurimide as said slip agent; and (2) said write-on film comprises a major amount of said low density polyethylene employed for said bag film, a minor amount of at least one polymer selected from the group consisting of EXXELOR# PA-30, EXXELOR# PA-50, with the proviso that said write-on film is substantially without slip agent, between about 3.0 wt.
% and about 20 wt. % of a calcium carbonate having a particle size distribution with about 50 percent of said particles less than 2 microns and about 30 percent of said particles less than 1 micron and said write-on film is embossed.
(1) said bag film is a low density polyethylene having a density between about 0.915 and about 0.930 grams per cubic centimeter containing between about 500 ppm and about 2500 ppm of ecurimide as said slip agent; and (2) said write-on film comprises a major amount of said low density polyethylene employed for said bag film, a minor amount of at least one polymer selected from the group consisting of EXXELOR# PA-30, EXXELOR# PA-50, with the proviso that said write-on film is substantially without slip agent, between about 3.0 wt.
% and about 20 wt. % of a calcium carbonate having a particle size distribution with about 50 percent of said particles less than 2 microns and about 30 percent of said particles less than 1 micron and said write-on film is embossed.
50. A stack of bags according to claim 33 or claim 34 or claim 49 wherein said corona-discharge treatment is between about 50 watts/in2 and about 150 watts/in2.
51. A stack of bags according to claim 33 or claim 34 or claim 49 wherein said bag is a closure-type bag.
52. A stack of bags according to claim 51 wherein said closure bag is a color-change closure bag having a translucent closure element and an opaque closure element on respective bag sidewalls.
53. A stack of bags according to claim 52 wherein said write-on film is on said sidewall of said closure bag having said translucent closure element.
54. A stack of bags according to claim 33 or claim 34 or claim 47 comprising a corona-discharge treated write-on film in contact with said bag film wherein the write-on film has a thickness of about 2.1 mils and said bag film has a thickness of about 0.7 mil.
55. A stack of bags according to claim 54 wherein the write-on film and bag film are formed by coextrusion.
56
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US44696689A | 1989-12-06 | 1989-12-06 | |
| US446,966 | 1989-12-06 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2030867A1 CA2030867A1 (en) | 1991-06-07 |
| CA2030867C true CA2030867C (en) | 1996-07-09 |
Family
ID=23774480
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2030867 Expired - Lifetime CA2030867C (en) | 1989-12-06 | 1990-11-26 | Write-on film surface and bags having a write-on stripe |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2030867C (en) |
-
1990
- 1990-11-26 CA CA 2030867 patent/CA2030867C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| CA2030867A1 (en) | 1991-06-07 |
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