JPH046026A - Sealing method for tube - Google Patents

Abstract

PURPOSE:To prevent a film or sheet from becoming thinner by a method wherein heat-seal is performed after preliminarily pressurizing folded parts on both sides of a tube locally in a temperature range which is lower than the melting point of a material but higher than the normal temperature. CONSTITUTION:In a process to bottom-seal or top-seal a tube shaped film or sheet with a thickness of not less than 100mum with folded parts at least on both sides, by performing preliminary pressurizing on the edge part by a heat plate in a temperature range which is lower than the melting point of a material (melting point-30 deg.C) and higher than the normal temperature for a thick film or sheet prior to heat-sealing by the hot plate swelling of the edge part can be prevented from happening. Therefore, at the following heat-sealing at a high temperature, heat-sealing under a condition in which thinning of the film or sheet does not generate at all becomes possible. For this reason, pin holes can be prevented from generating, and at the same time, the sealing strength can be drastically improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for sealing a polyolefin-based bottom seal or top seal bag that is free from pinholes and has improved seal strength.

[Conventional technology]

Polyolefin-based materials have recently begun to be used for medical liquid containers, particularly flexible soft bags, due to their safety and ease of use. However, these medical liquid containers (e.g., infusion bags, CAPD bags, etc.)
requires a very high level of quality, but at present it cannot be said that a sufficient level of performance has been reached yet. For example, in the bottom seal of a tubular film or sheet or the top seal with a spout, pinholes occur in the corner seals of the folded portions on both sides of the tube, causing problems such as poor quality.

[Problem to be solved by the invention]

The problems in the prior art are especially noticeable when sealing thick tubular films or sheets with a thickness of 100 microns or more. That is, as shown in FIG. 1, the ears (folded portions) of a thick tubular film or sheet are in a folded state, and therefore a large elastic recovery force acts on them.

Therefore, when the ear comes into contact with the hot plate for heat sealing, the bulge (ear) due to the elastic recovery force is first melted by the high temperature hot plate, and the ear is sealed before the inner surface is heat sealed. There was a problem in that pinholes were more likely to occur because the area around the interface between the sealed part and the non-sealed part became significantly thinner.

Particularly in fields where high quality is required, such as medical bags, it is absolutely necessary to prevent thinning of the film or sheet, which causes pinholes.

The problem to be solved by the present invention is to provide a sealing method that solves the problems of the prior art and prevents thinning of the film or sheet.

[Means to solve the problem]

As a result of extensive research in order to solve the above problems, the present inventors have discovered a heat sealing method that does not cause thinning of the corner seal portion of the ear even in thick tubular films or sheets with a thickness of 100μ or more. However, they succeeded in commercially producing an excellent medical bag and completed the present invention.

That is, the present invention provides a method for bottom-sealing or top-sealing a tubular film or sheet having a thickness of 100 μm or more and having folded portions on at least both sides. The present invention relates to a method for heat sealing a tube, which is characterized in that heat sealing is performed after pre-pressurizing at a temperature range higher than 30°C.

Polyolefin-based films or sheets are generally PV
It has a higher elastic modulus than C, and in particular, when the thickness is 100 μm or more, the elastic recovery force at the bent portion becomes large, and the ear portion (folded portion) of the tube in particular becomes greatly swollen. Therefore, if heat sealing is performed using a heated hot plate in this state, the hot plate will first come into contact with the swelled part of the ear before the inner surface of the tube is fused, and the surface will partially become fused. After melting, the inner surface will be sealed. At this time, due to partial melting of the surface of the film or sheet by the hot plate, the thickness of the film or sheet becomes thinner, which becomes a cause of pinhole generation later. In particular, when the thickness of a tubular film or sheet is reduced, it is necessary to increase the temperature of the hot plate or increase the sealing time in order to improve the sealing of the inner surface of the tube. On the other hand, from the viewpoint of productivity, it is not preferable to increase the sealing time, so the only option is to increase the temperature of the hot plate. However, it was found that as the temperature of the hot plate was increased, the thinning caused by the swelling of the ears became even greater.

For such thick films or sheets, the edges should be heated below the melting point of the material and (
By performing preliminary pressurization with a hot plate at a temperature higher than the melting point (-30° C.), swelling of the ears can be prevented.

Therefore, even in the subsequent heat sealing at high temperatures, it became possible to heat seal without thinning at all.

This makes it possible to prevent pinholes from occurring and to significantly improve seal strength.

The present invention will be explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

0 Length Example] For tubular films or sheets of various thicknesses of LDPE, L-LDPE, and PP, the sealing strength using JISZ 152B and the following definitions are determined depending on the presence or absence of pre-pressurization and the temperature of pre-pressurization. Examples] to 6 and Comparative Examples 1 to 7 in Table 1 show how the thinning rate changes.

Note that the ear thinning rate was defined by the following formula.

Thinning rate (%) = ((a-bL/al xlOO
Here, the position of the m leg of the thinning is a position 1 m+s into the sealed part from the boundary between the sill part and the non-sealed part of the ear part (bent part) of the bottom seal, as shown in Fig. 2. A cross-sectional view taken along the arrow in FIG. 3 is shown in FIG.

As shown in FIG. 3, the thickness a of the film or sheet in the non-sealed portion and the thickness b of the film or sheet at the thinnest portion in the non-sealed portion were measured, and the thinning rate was determined using the above formula.

As in Comparative Example 1, in the case of a tubular film with a relatively thin thickness, the thinning rate of the edge portion is not so large even without pre-pressing, but in the case of a tubular sheet with a thickness of 200+ am or more, pre-pressing However, if the temperature of the pre-pressurization is lower than the temperature range of the present invention, the thinning rate of the ear portion becomes large (Comparative Examples 2 to 6).

Further, when the temperature of heat sealing is lowered as in Comparative Example 7, the thinning rate of the ear portion is small, but the sealing strength is low and it is not usable.

On the other hand, it is clear that in Examples 1 to 6, in which preliminary pressurization was performed within the temperature range of the present invention, the thinning rate of the ear portion was low and sufficient seal strength was obtained. .

〔Effect of the invention〕

If a tubular film or sheet with a thickness of 100 μm or more is sealed by the method of the present invention, a bag with few pinholes and sufficient sealing strength can be obtained.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the ears (folded parts) at both ends of a tubular film or sheet with a thickness of 100μ or more.
1 is an overall view, and (b) is a cross-sectional view taken along line A-A'. Figure 2 shows an example of a bottom seal bag and the thinned part, 71 dollars
It is a figure which showed the cutting position (BB') at 1 regular time. FIG. 3 is a cross-sectional view taken along line BB' in FIG. In Figure 3, the shaded area indicates the seal portion.

Claims (1)

[Claims] In a method for bottom-sealing or top-sealing a tubular film or sheet having a thickness of 100μ or more and having folded portions on at least both sides, the folded portions on both sides are partially lower than the melting point of the material and below (melting point -30°C). A tube sealing method characterized by heat sealing after pre-pressurizing in a high temperature range.