WO1999002324A1

WO1999002324A1 - Thermally imparting a pattern on an injection molded preform and blow molding it into a container

Info

Publication number: WO1999002324A1
Application number: PCT/US1997/015407
Authority: WO
Inventors: Martin H. Beck; Robert J. Caldicott; George F. Rollend
Original assignee: Dtl Imprint, Llc
Priority date: 1997-07-09
Filing date: 1997-09-03
Publication date: 1999-01-21
Also published as: AU4174997A

Abstract

A preform (1) is injection molded. Thermal energy such as radiant heat, convective heat, or ultraviolet energy is applied to the preform (1) to form a desired pattern (5) by altering the molecular morphology and optionally imprinting of the surface or subsurface of the portion to be patterned. The preform (1) is used to blow mold a container (3) having a shaped and/or colored pattern. The thermal energy changes the molecular morphology by crystallization, chain scission, degradation or melting. The thermal energy may be supplied by a heater, branding iron or laser.

Description

Thermally Imparting a Pattern on an Injection Molded Preform and Blow Molding it into a Container

FIELD OF THE INVENTION The present invention pertains to a process for producing a blow molded plastic container having a shaped and/or colored pattern in the subsurface and/or outer surface thereof. In particular, this invention pertains to a process of forming, using thermal energy, a shaped feature in or on the inner and/or outer surface of a plastic preform suitable for blow molding a plastic container, a preform having such a feature and/or colorant formed in or on the inner and/or outer surface thereof and a plastic container having a shaped and/or colored design in or on the inner and/or outer surface thereof produced from such a preform. 0

BACKGROUND OF THE INVENTION

The soft drink industry is a highly competitive industry that has long demanded an inexpensive bottle for packaging its products . Blow molded plastic bottles 5 presently provide the best available combination of structural integrity and economy of manufacture in the industry, and therefore dominate today's soft drink market. These plastic bottles are typically one piece self-standing bi-axially oriented two liter bottles formed 0 of a tough, flexible plastic, usually a polyester such as

PET. The structure of blow molded PET bottles and the process of blow molding PET bottles are well known in the industry and are therefore not described in detail herein.

The highly competitive nature of the soft drink 5 industry demands that bottles provide brand distinction.

Changing labels on the generically shaped PET bottles is simply not enough for today's soft drink market. Labels, while colorful and informative (product information, etc.), are costly to purchase, inventory and apply. In addition, labels are generally "flat" or two dimensional in appearance and do not add to the structural appearance or design of the bottle.

To increase brand distinction, Coca-Cola^® has gone to a contoured blow molded PET bottle design with ribbing. While Pepsi Cola^® has resorted to swirls on the shoulder, and 7-Up^® uses green colored bottles. Other brands likewise desire distinguishing features to identifying their brand or make their bottles stand out among the competition's bottles. Unfortunately, the cost of making selected tooling for each blow molded PET bottle shape, manufacturing and inventory becomes prohibitively expensive. Further, additional material is required to maintain the required structural integrity of a conventional modified PET container when subjected to internal pressurization from the carbonated beverage contained in therein. Decorative patterns are presently molded into PET bottles during the blow molding process, i.e. the structural design of the bottles is shaped by specially designed blow molds . Patterns that have been blow molded into the bottles may frequently have an adverse effect on the structural integrity and strength of the bottles. When a blow molded bottle is filled with a carbonated beverage, the plastic walls tend to yield (creep) due to the internal pressurization of the container, particularly in areas that are weakened by a conventionally blow molded design. The yielding of the bottle upon carbonation causes the patterns that have been costly blow molded into the container to become diminished and/or distorted. Extra material is required in the area of the design to provide added wall strength and prevent diminution and distortion of the blow molded patterns .

At a market price for PET material of U.S. $0.75/ pound ($1.65/kg), one additional gram of resin per bottle adds $0.00165 to the cost of manufacturing each bottle.

If that cost is spread over 5 billion bottles then the increased cost will be more than $8,000,000 per year.

Each additional gram of PET per bottle would add $8 million to annual costs. It is an object of the present invention to provide a flexible inexpensive process of producing blow molded plastic containers having shaped decorative and/or patterns .

It is a further object of the invention to provide a process that reduces the quantity of material required to form a shaped decorative or pattern on a blow molded plastic container, while maintaining the structural integrity of the container.

SUMMARY OF THE INVENTION

The objects of the present invention are achieved by forming a shaped feature, by the use of thermal energy, onto the inner surface and/or outer surface of a preform suitable for blow molding a container exhibiting the desired shaped design.

According to the invention there is provided a process of producing a hollow plastic preform suitable for blow molding a plastic container having a desired shaped design on at least one of an outer and inner surface of the container, comprising the steps of: a) injection molding a hollow plastic preform suitable for blow molding a plastic container; and b) applying thermal energy to form a shaped feature on corresponding at least one of an inner surface and an outer surface of the preform, the shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired shaped design on the at least one of an outer and inner surface of the container. Also according to the invention there is also provided a hollow plastic preform, suitable for blow molding a plastic container, having a shaped feature formed by thermal energy on at least one of an outer surface and inner surface of the container produced by the above process, and a container blow molded from such a preform.

Further according to the invention there is also provided a process of blow molding a plastic container having patterns on at least one of an subsurface and an outer surface of the container from a preform produced according to the above process .

Further according to the invention there is a process of producing a hollow plastic preform suitable for blow molding a plastic container having a desired intaglio design on at least one of an outer and inner surface of the container, comprising the steps of: a) injection molding a hollow plastic preform suitable for blow molding a plastic container; and b) forming an intaglio shaped feature by laser cutting into at least one of an inner surface and an outer surface of the preform, the intaglio shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired intaglio design on the at least one of an outer and inner surface of the container. Further according to the invention there is a process of producing a blow molded plastic container having a desired intaglio design on at least one of an outer and inner surface of the container, comprising the steps of: a) injection molding a hollow plastic preform suitable for blow molding a plastic container; b) forming an intaglio shaped feature by laser cutting into at least one of an inner surface and an outer surface of the preform, the intaglio shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired shaped design on the at least one of an outer and inner surface of the container,- and c) blow molding the preform into a container having the desired intaglio design on the at least one of an outer and inner surface of the container.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying Figures, in which:

Fig. 1 is a simplified cross-sectional view of an injection molded plastic preform that has been imprinted with shaped design features according to the present invention, along with a bottle having shaped design features produced from such an imprinted preform, in which the thickness of the walls of the preform and container and the depth of the imprinted design features have been exaggerated for illustration purposes;

Fig. 2 is diagrammatic illustration of a preform having a design feature imprinted an a surface thereof along with a container blow molded from such a preform, showing the degree of stretch of the design; and

Figs. 3, 4 and 5 are fragmentary cross-sectional views of blown container walls having shaped designs formed thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the Figure 1, the surface of an injection molded plastic, for example, PET, preform 1, suitable for blow molding into a plastic container 3, is formed with shaped design features 5, such as swirls, ridges, ribs, designs and/or textured areas which may be recessed, for example, by pressing a branding iron into the inner and/or outer surface of the preform 1. The branding iron is contoured radially and longitudinally to the surface of the preform 1 to be imprinted and the surface of the branding iron is a relief of the shaped features 5 to be imprinted on the preform. The branding iron may have surfaces at two or more levels for imprinting design features 5 of different depths in a single imprinting step.

To imprint the design features 5 into the preform 1, the branding iron is heated to a temperature of about 300°F to about 330°F and is pressed against the surface of the preform to be imprinted for ^ to 3 seconds at a sufficient pressure to form the shaped features 5. The amount of time and pressure required to imprint the design features 5 into the surface of the preform depend upon the area, contour, depth, etc. of the design features 5.

The design features 5 are imprinted to a depth of 0.0005 inches (0.0127 mm) to 0.050 inches (1.27 mm) into the surface of the side wall 9 of a typical preform 1 having a wall thickness in the range of from about 0.135 inches (3.429 mm) to about 0.165 inches (4.191 mm). With this construction, the shaped design features 5 are relatively shallow, compared to the thickness of the side wall 9 of the preform.

When the preform 1 is blow molded into a container 3, the walls 9 of the preform l are stretched and thinned by a factor of up to 15x, thereby producing a container 3 having a typical wall thickness of approximately 0.008 inches (0.203 mm) to 0.015 inches (0.381 mm) . The design features 5 are stretched and thinned along with the wall 9 of the preform 1 during blow molding, as shown with dashed lines in Fig. 2. The design features 11 in the resulting container 3 are therefore relatively shallow, compared to the thickness of the wall 13 of the container 3 , and do not extend into the inner region of the wall 13. As a result of the relatively shallow depth of the design features 11, the design features 11 according to the invention do not significantly adversely affect the structural integrity of the container 3. Only the surface of the blow molded container 3 is affected by the imprinted design features . No additional material is required to prevent the design features 11 according to the present invention from diminishing or distorting upon internal pressurization of the container 3. Thus, a reduction in material is achieved compared to existing methods of producing design features on blow molded containers .

When blow molded into a container 3, the design features 5 imprinted on the preform will increase in size by a factor of 2-13x, depending on stretch ratios and location of the design features 5 on the resulting blow molded container 3. The location, size, shape and configuration of the design features 5 to be imprinted on the preform 1 must therefore be designed to accommodate the stretch ratios and location of the desired design features 13 on the resulting blow molded container 3.

The shaped design features 5, 11 can be provided on the outer surface 15, 17 only of the preform 1 and resulting container 3, inner surface 19, 21 only, or a combination of both the outer 15, 17 and inner 19, 21 surfaces . Imprinting the design features 5 on the inner surface 19 of the preform 1 will provide the illusion of depth to the design 11 in the resulting container 3. The illusion of depth of the design 11 in the resulting container 3 can be enhanced by imprinting both the outer 15 and inner 19 surfaces of the preform 1. Providing an offset, as illustrated in the Figure, between the outer and inner design features 5 further enhances the perception of depth of the design 11 in the resulting container 3 while maximizing retention of wall strength in the resulting container. Moreover, the container 3 can be provided with a tactile feel by placing a design feature 5 on the outer surface 15 of the preform 1, so that the design 11 on the outer surface 17 of the resulting container 3 retains a surface texture shaped design feature 5,13 may be located anywhere on the preform land resulting container 3 as desired, i.e. on the sidewall, base, feet and/or neck portions, for example. Portions of the surface of the container 3, the design features 11, and/or recessed panel 23 on the container 3 may be colored by embedding a colorant into the outer 15 and/or inner 19 surface of the preform with the branding iron during the imprinting step. The colorant is a concentrated colorant, such as a master batch additive at the same concentration that is conventionally used when coloring an entire preform to producing a colored container.

In order to embed colorant in the surface of the preform 1, the hot branding iron is dipped into beads of colorant, such that the beads of colorant melt and adhere to the branding iron before imprinting the shaped design features 5 into the preform. The melted colorant then becomes embedded in the surface of the preform during the subsequent imprinting step. In this manner, the surface of the preform is imprinted with the shaped design features with colorant embedded therein in a single imprinting step for producing colored features and shaped features 11 on the resulting container 3. During blow molding, the area of the colored feature may be increased by a factor of about lOx thereby reducing its thickness by a factor of about lOx.

The colorant may be adhered to the branding iron only on a surface of the branding iron that forms a shaped design feature on the preform 1, for coloring at least a portion of a shaped design feature 11 on the container 3. Moreover, different colored colorants may be adhered to different portions and/or different levels of the branding iron and embedded into different areas of the preform 1, for producing differently colored features, differently colored shaped features 11 or any desired combination of colored features and colored shaped features 11 on the surface of the container 3. The present invention provides a process of producing decorative blow molded containers having design features that alter the geometry of the inner and/or outer surface of a blow molded container without detrimentally effecting the structural integrity of the container. Since design features produced by the present invention do not effect the structural integrity of the container, there is no need to provided additional material to strengthen the container in the area of the design feature. Thus, the present invention reduces the amount of material required to produce blow molded containers having shaped design features on the inner and/or outer surfaces thereof, compared to conventional methods of blow molding such features into the surface of a container. In fact, by the use of suitably shaped imprint patterns, container produced by the present invention may have enhanced strength without any associated weight increase.

In an alternative embodiment internal energy is associated with altering the morphology of a preform to produce a visible or invisible design on a preform which ultimately becomes a visible image on a blown article. The visible or invisible design on a preform made by thermal energy is a thermal image which ultimately becomes a visible image on a blown article, which may be a visible design on a preform composed of depressions or indentations . "Preform Imaging" involves input of mechanical or thermal energy to form an image on the intermediate preform which when blown into an article results in an optically apparent image. Mechanical imaging consists of supplying mechanical energy (work) to displace or remove thermal energy to create images of altered morphology which are sometimes also intaglio in nature . Use of directed thermal energy can alter the morphology without creating an intaglio image. Thermal energy may be introduced by several means, such as but not limited to radiant, convective, conductive or ultrasonic.

The present invention also provides a process of producing decorative blow molded containers having patterns that alter the geometry of the inner and/or outer surface structure of a blow molded container without detrimentally effecting the structural integrity of the container.

In this embodiment of the present invention thermal imaging consists of applying thermal energy to a preform to create optically apparent images of altered molecular morphology on the final blow molded container. While use of thermal energy can alter the morphology without creating an intaglio design it is also possible to create a pattern which is intaglio in nature. Thermal energy may be introduced by several means, such as but not limited to radiant, convective, conductive or ultrasonic energy .

An optically apparent image is a design or pattern that may be viewed in visible light (400-750 nm) and is distinct from its surrounding or background (the non-imaged portion) . The two ways which the optically apparent image is distinguished from its background upon its interaction with visible light are differences in 1) color or 2 ) spatial distribution of light. Color is composed of hue, saturation and lightness. Spatial distribution of light is composed of diffuse and specular reflection as well as diffuse and regular transmission. The percent of each sub category of color and spatial distribution of light determines the appearance of an image. Differences in color as well as spatial distributions of light are initiated in the imaging phase whereby the introduction of energy induces changes in morphology by many possible mechanisms, most commonly: chain scission, volatization, melting, crystallization and degradation.

A non-imaged, blown container is for the most part transparent, in that most visible light passes through it via regular transmission. Upon applying thermal energy in the process of thermal imaging, morphology changes take place which typically result in a decrease in the regular transmission and an increase in diffuse transmission and diffuse reflection. As these light distributions change, the image changes from transparent to translucent, to slight opaque and finally to complete opacity. The opacity of the image compared with the transparent background makes for a distinct optically apparent image which is clearly visible to the human eye.

For example, increased crystallinity represents tighter packing of molecular chains, which decreases regular light transmission and increases diffuse transmission and diffuse reflection, ultimately yielding a white appearance . Another example leading to increase opacity is that associated with volatization of the polymer. Volatization occurs during degradation of the polymer chains which may lead to many things such as the creation of oligomers, shorter chains and increased crystallinity . During volatization, some of the volatized polymer may cling to the image by way of electrostatic charge, mechanical interlocking, diffusion or adsorption. Changes in color and spatial distributions in the area of an image has often, but not always (depending on the degree of morphology changes) , been known to result in increased preform temperature during the reheat step stretch blow molding process. This is a result of increased energy absorption from changes in index of refraction and light transmission reflection. In some cases, temperature increases as high as 15 degrees Celsius have been observed.

Using laser etching techniques to vary the degrees of transparency, diffusion and reflection, creates patterns having illusions of depth with highlights and the like. Further, combining morphology changes with depth and specific designs will yield images with specular reflection that will to the eye, appear as sparkles, holographic illusions and the like. Thus laser etching creates visible images by changing the degree of transparency, diffusion and reflection through morphology changes, degrees of morphology, depth and combinations of these techniques .

Figs. 3 and 4 illustrate intaglio patterns formed in the outer wall of a container with an underlying crystallized layer shown by dark stippling. Fig. 5 illustrates how morphology changes are not necessarily coincident with intaglio characteristics . The pattern 5 created by altered morphology exists in the surface and subsurface (dark stippling) of the container wall 3 without the removal of preform material and the creation of intaglio characteristics.

This method of pure interaction of energy with the preform may also be utilized to alter the color of the pattern by adjusting the morphology of the pattern to acquire a desired hue, saturation and lightness. In addition color changes may be achieved by incorporating energy sensitive materials into or on the preform, which change color upon interaction with specific types and magnitudes of energy. Colorants may also be applied before, during or after the pattern is thermally derived.

Portions of the surface of the container 3 that are blown, i.e. stretched, such as recessed panel 7, for example, can also be lightly crystallized, turning these portions slightly white to the eye. By appropriately locating crystallized portions on the container 3, the aesthetics of the design or the container 3 can be enhanced by including clear and white portions as part of the design. In order to form white crystallized portions on the resulting container 3, small localized areas on the outer 17 and/or inner 21 surface of the preform 1 that are to be blown and stretched during blow molding are heated by the addition of thermal energy during the formation of the pattern to initiate, but not complete, the desired crystallization, forming crystal initiating sites. Due to the relatively small localized nature of crystal initiating sites on the surface of the preform, the preform looks transparent to the naked eye. Upon subsequent heating and blow molding of the preform 1, the crystal initiating sites 25 cause areas of the surface of the container 3 to crystalize to a depth of 0.0005 inches (0.0127 mm) to 0.005 inches (0.127 mm). The crystallization may, however, extend entirely through the wall of the container 3. By appropriately locating the crystal initiating sites 25 on the preform 1 in relation to an imprinted pattern, in this case the recessed panel 7, for example, a white pattern, for example, a snowman, star 11 (Fig. 2) or, a white recessed panel 7 (Fig. 1) , can be produced on the surface of the resulting container 3. Portions or all of the shaped patterns 11 on the container 3 may be made white by appropriately locating the crystal initiating sites 25 on the surface of the preform 1. Upon being crystallized, the crystallized portions of the wall 13 of the container 3 become more rigid than the uncrystallized portions of the container 3. Less material is therefore required to provide a crystallized pattern with the required strength to prevent distortion of the pattern upon internal pressurization of the container, providing further reductions in material .

In continuing physical tests of bottles having shaped patterns produces according to the present invention containing four volumes of carbonation at 100°F, the patterns on the bottles have insignificant distortion with pressure or temperature over a period of approximately 168 hours .

Although laser etching and branding with a branding iron are the methods disclosed herein for imprinting the shaped patterns 5 into the preform 1, other suitable thermal energy imparting methods may be employed to imprint the patterns into the surface (s) of the preform. The patterns may be imprinted, for example, by using other methods of thermal energy including but not limited to radiant, conductive, convective or ultrasonic energy, or by any combination of such methods. The method of imprinting a design that covers the entire circumference of the interior and/or exterior surfaces of the preform can be accomplished in several ways. The preform may be rotated 360° while being imprinted by a stationary device, for example, or the imprinting device may orbit 360° around a stationary preform. Also the preform may be appropriately temperature conditioned to facilitate the imprinting.

The term "imprinting" , as used throughout the specification and claims, is intended to include any suitable method for forming a shaped pattern in the inner and/or outer surface of a preform 1 suitable for blow molding a container.

Claims

In the Claims :

1. A process of producing a hollow plastic preform suitable for blow molding a plastic container having a desired shaped design on at least one of an outer and inner surface of the container, comprising the steps of: a) injection molding a hollow plastic preform suitable for blow molding a plastic container; and b) applying thermal energy to form a shaped feature on corresponding at least one of an inner surface and an outer surface of the preform, the shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired shaped design on the at least one of an outer and inner surface of the container.

2. The process according to claim 1, wherein step b) comprises imprinting the shaped feature into the surface of the preform to a depth such that, upon blow molding the imprinted preform into a container, the shaped design in the container has an insignificant affect on structural integrity of the container.

3. The process according to claim 1, wherein step b) comprises applying thermal energy to a portion of the preform to create said shaped feature by altering the molecular morphology at least one of the outer surface and inner surface of the preform.

4. The process according to claim 1, further comprising the step of forming a crystal initiating site on at least one of the inner and the outer surface of the preform, and causing an associated portion of the surface of the container to crystalize, turning the portion white.

5. The process according to claim 1, wherein the thermal energy is applied by radiant energy means.

6. The process according to claim 1, wherein the thermal energy is applied by convective energy means.

7. The process according to claim 1, wherein the thermal energy is applied by ultra sonic energy means.

8. The process according to claim- 1, wherein the thermal energy is applied by conductive energy means.

9. The process according to claim 1, wherein the thermal energy is applied by laser etching means.

10. The process according to claim 1, wherein said shaped feature is formed intaglio with the surface of the preform.

11. A process of producing a blow molded plastic container having a desired shaped design on at least one of the outer and inner surface of the container, comprising the steps of: a) injection molding a hollow plastic preform suitable for blow molding a plastic container; b) applying thermal energy to form a shaped feature on corresponding at least one of the outer surface and inner surface of the preform, the shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired shaped feature on the at least one of the outer and inner surface of the container; and c) blow molding the preform into a container having the desired shaped design on at least one of the outer and inner surface of the container.

12. A blow molded plastic container having a shaped design on at least one of the outer and inner surface of the container produced by a process according to claim 11.

13. The process according to claim 3, wherein the molecular morphology of said preform is altered by chain scission to produce the shaped feature.

14. The process according to claim 3, wherein the molecular morphology of said preform is degraded to induce volatization to produce the shaped feature.

15. The process according to claim 3, wherein the molecular morphology of said preform is altered by melting to produce the shaped feature .

16. The process according to claim 3, wherein the molecular morphology of said preform is altered by initiating crystallization to produce the shaped feature.

17. The process according to claim 14, wherein said volatization produces a volatized product which clings to said shaped feature .

18 A process of producing a hollow plastic preform suitable for blow molding a plastic container having a desired intaglio design on at least one of an outer and inner surface of the container, comprising the steps of: a) injection molding a hollow plastic preform suitable for blow molding a plastic container; and b) forming an intaglio shaped feature by laser cutting into at least one of an inner surface and an outer surface of the preform, the intaglio shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired intaglio design on the at least one of an outer and inner surface of the container.

19. A process of producing a blow molded plastic container having a desired intaglio design on at least one of an outer and inner surface of the container, comprising the steps of : a) injection molding a hollow plastic preform suitable for blow molding a plastic container; b) forming an intaglio shaped feature by laser cutting into at least one of an inner surface and an outer surface of the preform, the intaglio shaped feature being sized, shaped and oriented on the preform to, upon blow molding the preform into a container, produce the desired shaped design on the at least one of an outer and inner surface of the container; and c) blow molding the preform into a container having the desired intaglio design on the at least one of an outer and inner surface of the container.