JPH0353100B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field> This invention relates to a sheet for forming a shrinkable sleeve,
Specifically, it relates to a sheet that is used as a material for shrink sleeves for covering and protecting glass bottles for storing liquid foods and drinks such as youth, alcoholic beverages, and soft drinks. <Prior art> A shrink sleeve made of a heat-shrinkable thermoplastic resin sheet is placed on the outer surface of the glass bottle for beverages, etc., and then the shrink sleeve is shrunk by heating. Glass bottles are often coated closely along their outer surface to provide cushioning protection during transportation and storage of glass bottles. The properties required of the sleeve forming sheet for forming this shrink sleeve include good shrinkage performance for the bottle external shape, impact resistance against bottle breakage, cushioning protection performance such as tensile strength, and bottle fragments when the bottle breaks. There are properties such as anti-scattering performance and printability. The applicant has developed a sheet that has improved impact resistance and has good transparency compared to thermoplastic resin sheets made of various resins such as polystyrene and polyvinyl chloride, which have been used as sheets for forming sleeves in the past. In other words, Japanese Patent Application No. 1983-79892 was previously filed as a material capable of exhibiting printability. However, even in the above-mentioned prior art and conventional ordinary sleeve forming sheets, when the glass bottle is used after the shrink sleeve is shrink-coated on the glass bottle, the glass bottle filled with drinking water etc.
When sterilized and washed with high-temperature hot water, glass bottles and shrink sleeves may differ in thermal expansion coefficient and deteriorate when exposed to outside air after hot water treatment.
Cracks sometimes appeared along the circumferential direction of the shrinkable sleeve. This crack not only spoils the appearance of the glass bottle covered with the shrink sleeve, but also lowers the impact resistance and safety when the bottle is broken, causing the problem that the shrink sleeve cannot sufficiently protect the glass bottle. The occurrence of cracks after hot water treatment is
The degree of occurrence varies depending on the shape of the glass bottle, and it is not so much of a problem when shrink coating is applied to the body of a simple cylindrical bottle, but for example, as shown in Figures 1 to 3, When the shrink sleeve S covers the glass bottle G up to the narrow neck (Fig. 1), when the body of the glass bottle G is constricted (Fig. 2), the shrink sleeve S covers the glass bottle G up to the bottom of the glass bottle G.
The more complicated the shrinkage structure is, where the degree of shrinkage differs in the axial direction, such as when covering a shrinkable sleeve (FIG. 3), the more likely cracks will occur, and improvements have been desired. Therefore, we researched the cause of the above-mentioned cracks and found that with conventional shrink sleeves, the shrink sleeve is contracted along the radial direction of the glass bottle to tightly cover the glass bottle, and in most cases the shrink sleeve does not cover the glass bottle in the axial direction. It is designed not to shrink. Therefore, if a rapid temperature change is applied through hot water treatment, the expansion and contraction in the axial direction cannot be adequately coped with, and deterioration is also added, causing cracks. Cracks due to the above causes occur in a direction perpendicular to the axial direction of the shrinkable sleeve, that is, along the radial direction. Therefore, if the shrinkable sleeve is designed to shrink to some extent not only in the radial direction but also in the axial direction, the above problem will be solved. However, if the shrink sleeve shrinks in the axial direction, it will shrink in the axial direction before the radial direction when the glass bottle is heat-shrinked, causing wrinkles to appear in the shrink sleeve after shrinkage, or There is a problem that variations in length in the direction occur, resulting in an unsightly appearance and loss of product value.Also, the shrink sleeve is not long enough to cover the glass bottle sufficiently in the height direction. First, there was also the problem that the protective effect on glass bottles was reduced. <Purpose> Therefore, the purpose of the present invention is to solve the problems of the above-mentioned prior art and to obtain a sheet for forming a sleeve. Forming a shrink sleeve that satisfies various performance requirements, especially preventing cracks caused by hot water treatment, wrinkles during shrink coating, and no large shrinkage in the length direction of the glass bottle. The purpose is to provide a sheet for use. <Structure> The structure for achieving the above object is a stretched sheet extruded from a polystyrene resin containing 10 to 40% by weight of polybutadiene block aggregates with a diameter of 0.05 to 0.01μ, The shrinkage rate in the direction is 30% or more, and the shrinkage rate in the width direction is 5
~25%, and the shrinkage start temperature in the width direction is 3° C. or more higher than the shrinkage start temperature in the machine direction. <Example> Next, an example of the present invention will be described below. The sleeve-forming sheet of the present invention is formed by extrusion molding using polystyrene-based resin as a material, and by stretching the sheet, it has heat shrinkability that shrinks when heated.
It is a shrinkable sheet. Examples of the above-mentioned polystyrene resins include simple polystyrene resins, styrene polymers obtained by polymerizing aromatic monomers such as vinyltoluene, isopropylstyrene, α-methylstyrene, nuclear methylstyrene, chlorostyrene, and tertiary-butylstyrene; Styrene monomer, 1,3 butadiene, butyl acrylate, ethyl acrylate,
Alkyl acrylates such as 2-ethylhexyl acrylate, methyl methacrylate, butyl methacrylate, alkyl methacrylates such as 2-ethylhexyl methacrylate, acrylonitrile, vinyl acetate, α-methylethylene, divinylbenzene, dimethyl maleate, diethyl maleate A styrene copolymer containing 50% by weight or more of a styrene monomer obtained by copolymerization with a styrene monomer is used. Note that the degree of polymerization of the polystyrene resin used is about 900 to 2000. The lower the degree of polymerization, the better the gloss and transparency, and the better the appearance, and the easier it is to stretch, making it easier to control shrinkage.
This is the preferred practice. Further, it is preferable that the polystyrene resin has an MI value (melt index) of 3 or more.
This MI value indicates the fluidity of the resin, and when the MI value is 3 or less, the fluidity is low, so the extrusion temperature must be raised during extrusion molding, and the gelation of the rubber content, which will be described later, progresses. This is not preferable because it becomes difficult to set the particle size of the rubber component within a predetermined range. The styrene resin contains 10 to 40% of polybutadiene block aggregates having a diameter of 0.05 to 0.01 μm as a rubber component. As the diameter of the polybutadiene block aggregate increases, the impact resistance improves, but the transparency deteriorates.
The smaller the diameter, the better the transparency but the lower the impact resistance. And those in the above diameter range are
The impact resistance and transparency necessary for a sheet for forming shrinkable sleeves can be most effectively exhibited. Also,
The higher the content of polybutadiene block aggregates contained in the styrene resin, the better the impact resistance, but if it exceeds 40% by weight, it will not be able to provide sufficient stretching effect, so it is necessary as a sheet for forming sleeves. This is undesirable because it cannot exhibit sufficient shrinkage properties and is easily attacked by printing ink solvents during printing. Furthermore, the sheet for forming a shrinkable sleeve of the present invention may contain a plasticizer, a lubricant, a spreading agent, and other conventional additives. For example, when an ultraviolet deterioration inhibitor, a heat deterioration inhibitor, etc. are added, the crack prevention effect is further improved. A sheet for forming a shrinkable sleeve made from a styrene resin having the above composition has a thickness.
A thickness of 50 to 150μ is preferable. The thicker the thickness, the better the cushioning protection against glass bottles, etc.
Shape retention when forming a sleeve also improves, making it easier to perform shrink-coating work on glass bottles, etc. However, if the sleeve exceeds 150 μm, it becomes difficult to coat tightly along the complex external shape of the glass bottle, and it becomes difficult to apply heat-sealing. This is not preferable because it becomes difficult to join the ends of the sleeve and the manufacturing cost increases.
In addition, if the thickness is less than 50μ, the cushioning protection will be poor, and the shrink coating workability for glass bottles etc. will be poor.
This is not preferable because it impairs bottle windability. Next, the shrink sleeve is wound into a cylindrical shape and coated on a glass bottle, etc., and is heat-shrinked mainly in the radial direction to make it adhere tightly to the glass bottle. It is necessary to shrink significantly in the direction of That is, the styrene-based resin is extruded and drawn while being cooled and stretched at the same time to produce a sheet for forming a shrinkable sleeve. A stretched sheet that is greatly stretched in the machine direction is manufactured by adjusting the The greater the amount of stretching, the greater the shrinkage of the produced sheet for forming a shrinkable sleeve when heated. should be 30% or more in the flow direction. If the shrinkage rate in the machine direction is less than 30%, the shrink sleeve will not fit tightly along the outer shape of the glass bottle, etc., and it will not be possible to reliably cover the glass bottle with shrinkage. In addition, the shrinkage rate in the width direction is set to be 5 to 25%, and if the shrinkage rate in the width direction is less than 5%, it will not be possible to prevent the occurrence of cracks due to hot water treatment, and the shrinkage rate will be 25%. If this happens, the shrink sleeve will shrink significantly in the axial direction, making it impossible to reliably cover the required length of the glass bottle in the axial direction, and the axial ends of the covered shrink sleeve becoming wavy and dirty. etc., the performance as a shrinkable sleeve cannot be fully demonstrated. Furthermore, in the stretching process for imparting shrinkability, the sheet for forming a shrinkable sleeve is stretched in the width direction and in the machine direction separately, and preferably, after stretching in the width direction, the sheet is stretched in the machine direction. Perform stretching processing. Moreover, once the stretching process is performed in the width direction and the machine direction simultaneously, the stretching process may be further performed only in the machine direction. Moreover, the final stretching temperature during the width direction stretching process is set to be higher than the heating deformation temperature, and the stretching temperature during the final stretching process in the machine direction is set at least 3°C higher than the final stretching temperature in the width direction. Apply stretching. By performing the stretching process under these conditions, a sheet for forming a shrinkable sleeve that exhibits the shrinkage performance unique to this invention can be obtained, and when the sheet for forming a shrinkable sleeve is heated, it starts to shrink in the width direction. The temperature is 3℃ lower than the shrinkage start temperature in the flow direction.
If the sheet becomes higher than that, the shrinkage starts in the machine direction of the sheet, and the shrinkage in the width direction starts later than in the machine direction. In addition, in order to provide the above stretching conditions,
For example, when manufacturing a sheet for forming a shrinkable sleeve by inflation molding, stretching in the width direction is performed at the same time as inflation extrusion, then stretching in the machine direction is performed, and the stretching temperature in the width direction is All you have to do is change the stretching temperature in the machine direction. Further, when a T-die is used to extrude a sheet for forming a shrinkable sleeve, the sheet is stretched in the width direction at the same time as extrusion from the T-die, and then stretched in the machine direction. Furthermore, when using plug extrusion,
After stretching in the width direction at the same time as extrusion, stretching in the machine direction may be added. Among the physical properties of the sheet for forming shrinkable sleeves manufactured as described above, elongation rate is
6.5% or more, preferably 13.0% or more in the width direction. If this elongation rate is small, the shrink sleeve will not be able to absorb the impact energy well when a glass bottle, etc. covered with a shrink sleeve breaks, and the bottle fragments will fly far away, which is dangerous. Unfavorable from a safety point of view. In addition, the tensile strength is 1.5 to 8 kg in the flow direction,
It is preferable that the weight in the width direction is 1.0 to 6 kg. The higher the tensile strength, the more difficult the sleeve will be to tear, and the better the cushioning protection for the glass bottle will be. However, if the tensile strength is too high, when the glass bottle etc. breaks, the shrink sleeve will tear, gradually dissipating the impact energy. This is undesirable because the impact-reducing effect cannot be achieved and the bottle fragments scatter like cannonballs at the same time as the shrink sleeve breaks. Therefore, by keeping both the above elongation and tensile strength values within appropriate numerical ranges, the shrink sleeve can improve both its shock-absorbing protection and its ability to prevent bottle fragments from scattering when the bottle is broken. It is also possible to form a good product. Further, it is preferable that the falling ball impact value is 70 mm or more. The falling ball impact value is expressed as the height at which the sheet does not break when a steel ball is dropped onto the sheet surface, and the higher the falling ball impact value, the higher the cushioning protection against impact forces applied to glass bottles, etc. The sheet for forming a shrinkable sleeve of the present invention has the composition and physical properties as described above, but may have other properties depending on the use and purpose.
Appropriate components such as colorants, antistatic agents, etc. can be added to the polystyrene resin that is the material of the sheet. The sheet for forming a shrinkable sleeve is printed or colored as appropriate on its surface, cut into a predetermined size, and both ends in the flow direction are joined by means such as thermal bonding to form a cylindrical shrinkable sleeve. It is something to do. When printing on items such as items, the durability of the printed surface can be increased by printing on the back side of the shrink sleeve so that it passes through the shrink sleeve and appears on the outside. It has good properties and is suitable. Furthermore, the above-mentioned shrink sleeve is applied to the outer periphery of a glass bottle, etc., and then heated from the surrounding area.
Shrinkage sleeves are shrunk in the radial direction to tightly adhere to the outer shape of glass bottles, etc., and are integrally coated to provide cushioning protection during transport and storage of glass bottles, ensure safety when bottles are broken, and improve appearance. It is. Note that the shape of the shrink sleeve and the shape and structure of the glass bottle to be shrink coated can be changed as appropriate in the same way as conventional ones, but especially if the shape of the bottle is complex and the diameter changes in the height direction. It is most effective for use when the shrinkage is severe or when the amount of shrinkage of the shrinkage sleeve varies greatly in the height direction. In addition, the shrink sleeve forming sheet of the present invention is a shrink sleeve that can be used to cover and protect glass bottles for shrinking various liquids, ceramic products, synthetic resin pipes, metal cans, etc. in addition to glass bottles for soft drinks. It is also applicable to <Effects> The sheet for forming a shrinkable sleeve of the present invention configured as described above has a polystyrene resin with a diameter
Since it is formed from a material containing 10 to 40% by weight of polybutadiene block aggregates of 0.05 to 0.01μ, it has very good impact resistance and excellent transparency. That is, conventionally, when impact resistance was improved by incorporating rubber, the transparency of the sheet was extremely reduced, resulting in poor appearance as a shrinkable sleeve, but this invention Since polybutadiene block aggregates with extremely small diameters are used in this method, there is almost no scattering of light inside the sheet, and transparency is not reduced. Therefore, when using the shrink sleeve forming sheet,
Transparency of the shrink sleeve is very important, especially when back printing is applied to the inner surface of the shrink sleeve and the printed pattern is transmitted through the shrink sleeve to appear on the outer surface. With a sheet for forming a highly shrinkable sleeve, the printed pattern printed on the inner surface remains extremely clear even after passing through the sheet, and can be made to appear on the outer surface. Further, the printed surface of this sheet for forming a shrinkable sleeve can be adhesively laminated on a foamed sheet for forming a shrinkable sleeve for use. Furthermore, the polybutadiene block aggregate has the effect of improving the elongation of the sheet for forming the shrinkable sleeve, improving the ability to prevent scattering of bottle fragments when a glass bottle or the like is broken, and increasing safety. The shrink sleeve-forming sheet has a shrinkage rate of 30% or more in the machine direction, and has sufficient shrinkage to reliably adhere to the outer shape of the glass bottle. Moreover, since the shrinkage rate in the width direction is 5 to 25%, it has appropriate shrinkability in the width direction as well, and no cracks occur during hot water treatment. However, as described above, by providing shrinkability in the width direction, when the shrinkable sleeve is shrink-coated on a glass bottle, the shrinkable sleeve may be wrinkled, or may be wrinkled in the height direction of the glass bottle. Although there is a problem that the length of the shrinkable sleeve is insufficient, in this invention, as a shrinkage condition for the sheet for forming the shrinkable sleeve, the shrinkage temperature in the width direction is set to 3°C lower than the shrinkage temperature in the machine direction.
By using a higher setting than above,
Prevents wrinkles and lack of length. That is, a sleeve-forming sheet having the above-mentioned shrinkage conditions has a property that shrinkage upon heating begins in the flow direction during extrusion molding, and shrinkage in the width direction begins later. Therefore, if a shrink sleeve is wound and formed with the flow direction of the sheet in the radial direction, and the glass bottle is shrink coated, the shrink sleeve will first start shrinking in the radial direction due to heating, and the shrink sleeve will become the glass bottle. Since the shrink sleeve is tightly coated to a certain extent and then shrinks in the height direction of the glass bottle, there is no need to worry about the shrink sleeve becoming loose and causing wrinkles. There is less possibility of shortages or variations in length in the height direction, and the glass bottle can be covered tightly to the required coverage area, shrink-covered neatly, and has a good appearance. ,
We can produce shrink-coated glass bottles with high commercial value. As mentioned above, it has the impact resistance, cushioning properties, and ability to prevent bottle fragments from scattering when the bottle is broken, which is necessary for a shrink sleeve, and at the same time, it does not cause any cracks even when treated with hot water, so it can be used without any cracks. In order to form a shrink sleeve or a shrink coated bottle with high performance or commercial value, it is possible to provide a sheet for forming a shrink sleeve that is extremely suitable. <Example> In order to demonstrate the effects of the shrinkable sleeve forming sheet of the present invention as described above, a practical product of the present invention and a comparative product were manufactured and various performance tests were conducted, and the results are shown in the table below. Shown below. In addition, both the test product and the comparative product use polystyrene simple resin as the polystyrene resin, and add polybutadiene block aggregate to the polystyrene resin in order to contain polybutadiene block aggregate that becomes the rubber component. A mixture of styrene-butadiene block copolymer resin consisting of a copolymer resin of aggregate and polystyrene resin was used. The average particle size of the polybutadiene block aggregates was 0.01 to 0.02 μm, and the MI value of the polystyrene resin used was about 6 to 8.

【table】

[Table] From the above test results, it was demonstrated that the product according to the present invention has excellent usability as a shrink sleeve, particularly in preventing cracks and in bottle winding properties. In addition, in Comparative Examples 1 and 5, cracks occur because the shrinkage rate in the width direction is less than 5%. In Comparative Examples 2 and 4, the contraction rate in the width direction was 25% or more, so wrinkles occurred when the bottles were rolled up. In Comparative Example 3, since the shrinkage rate in the machine direction was less than 30%, wrinkles occurred due to insufficient shrinkage. In Comparative Examples 6 and 7, the shrinkage start temperature was higher in the machine direction than in the width direction, so wrinkles occurred during bottle winding.

[Brief explanation of drawings]

1 to 3 are partially cutaway front views showing several examples of bottle shapes and contracted states in which the shrink sleeve is shrink coated.

Claims (1)

[Claims] 1 A stretched sheet extruded from polystyrene resin containing 10 to 40% by weight of polybutadiene block aggregates with a diameter of 0.05 to 0.01μ, with a shrinkage rate of 30% or more in the machine direction and a shrinkage rate in the width direction. 5
25%, and whose shrinkage start temperature in the width direction is 3° C. or more higher than the shrinkage start temperature in the machine direction.