JPH0211315A - Heat-molding of thermoplastic laminate sheet - Google Patents

Abstract

PURPOSE:To obtain uniformity in the distribution of air bubbles in a molded item by inserting a thermoplastic laminate sheet wherein a central layer is a foamed layer and both faces thereof are laminated with unfoamed films between hot plates and performing secondary foaming thereof by means of vacuum sucking. CONSTITUTION:A sheet prepd. by laminating e.g. polystyrene sheets on both upper and lower faces of a foamed polystyrene layer is used as a raw sheet 1. The raw sheet, namely a three-layered laminate sheet 1 is preheated in a heating oven 2 to make the raw sheet in a softened and plasticized state. Then, it is transferred in a foaming and heating zone 3 which is a heating device, which consists of two heating plates 4 and 5 having vacuum holes, between the circumference of the laminate sheet softened and having plasticity by heating is clamped and the clearance between these heating plates is made 1.5-5.0 times the softened raw sheet. The raw sheet foamed and heated between both heating plates is transferred in a molding zone 6, where it is molded into a molded product.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method of thermoforming a thermoplastic laminate sheet, and in particular to a method of thermoforming a thermoplastic laminate sheet, and in particular, a thermoplastic laminate sheet having a foam layer further foamed from a thermoplastic laminate sheet having a foam layer of low expansion ratio. The present invention relates to a thermoforming method for producing thermoplastic laminate molded products.

(Prior art) As a method of heat forming a foam molded product made of a thermoplastic foam sheet, the method usually involves extruding a thermoplastic synthetic resin mixed with a foaming agent into a foam sheet using an extruder, and then This is called primary foaming, and the resulting sheet is called primary foaming sheet, foam extrusion original fabric, or simply original fabric)
When this second foamed sheet is heated again in a heating oven or the like to increase the pressure of the foaming gas remaining within the sheet and the foamed sheet is molded at a temperature above its softening point, the pressure of the foaming gas acts as foaming pressure. , - The final molded product is obtained by foaming until the thickness becomes about 2 to 2.6 times the thickness of the secondary foaming sheet (this is called secondary foaming).

However, if the secondary foam sheet is stored for a long period of time, or if the primary foam sheet is a highly breathable primary foam sheet with few closed cells, - the foam gas remaining in the secondary foam sheet may is dissipated and replaced with air, making it impossible to obtain a foam molded product with a sufficient secondary expansion ratio. A secondary foamed molded product that does not have a sufficient secondary expansion ratio has insufficient strength and heat insulation properties, and cannot be said to be a satisfactory product.

As a means to solve these problems, the applicant first adjusted the space between the male and female molds so that there was an appropriate gap when obtaining a foam molded product, and heated the molds between the molds. Hold the softened foam sheet.

An application was filed for a method in which vacuum suction is applied from both sides of a mold to cause foaming within the mold and molding at the same time (see Japanese Patent Application No. 63-93244).

However, in this method, the mold temperature must be sufficiently lower than the heating softening temperature of the original fabric.

After molding, the molded product will be deformed.

For this reason, when vacuum foaming is performed in the mold, the surface of the molded product is cooled, so the foam concentrates in the center where the temperature is still high, causing a hollowing phenomenon and reducing the strength of the resulting molded product. However, in this method, the expansion ratio of the foamed extrusion original fabric is said to be limited to 1.5 to 2.0 times.

Furthermore, the molds used for molding must be male and female molds or pine molds whose clearances have been machined with high accuracy, which increases production costs.

(Problem M to be Solved by the Invention) The present inventor has improved the above-mentioned drawbacks, and has made it possible to sufficiently foam and heat a foamed sheet before molding, with almost no secondary foaming occurring during heating under normal pressure. This led to the discovery of a method and the completion of the present invention.

An object of the present invention is to provide a heat molding method for obtaining a secondary foamed sheet that can be further expanded to become a thicker and stronger molded product than a secondary foamed sheet.

(Means for Solving the Problems) That is, the present invention provides a thermoplastic laminate having a three-layer structure consisting of a foam layer with a foaming ratio of 1.5 to 3.0 times, and non-foaming films laminated on both sides of the foam layer. Sheet 110-190
After softening by heating to ℃, the sheet is inserted between hot plates whose clearance is adjusted to 1.5 to 5.0 times the thickness of the softened thermoplastic laminate sheet, and the peripheral edge of the thermoplastic laminate sheet is sealed. At the same time, the air between the hot plates is evacuated and the pressure is reduced to foam the foam layer, and the double-sided film layer of the thermoplastic laminate sheet is heated so as to be in close contact with each hot plate. This method of thermoforming a thermoplastic laminate sheet is characterized in that the thermoplastic laminate sheet is taken out from between the plates and molded into a molded article having a desired shape.

The material used in the present invention is a thermoplastic laminate sheet having a three-layer structure with a foamed center layer and non-foamed films laminated on both sides.

Even if vacuum is drawn from the heating plate side, cavitation in the foam layer can be avoided, and even after the residual gas has dissipated due to long-term storage of the foam sheet, it is possible to cause secondary foaming, which can be thermoformed. By doing so, it is possible to mold a molded product with excellent strength and heat insulation properties.

The present invention will be explained in more detail.

First, the material used in the invention is a laminated sheet having a three-layer structure made of thermoplastic sheets, as described above. The thermoplastic resin used in the present invention is a polyolefin resin, a polystyrene resin, or a mixed resin of both resins. Examples of polyolefin resins include polypropylene, polyethylene, polybutene, polymethylpentene, mixtures of these polymers, ethylene/vinyl acetate copolymers containing 50% or more of olefins, ethylene/methacrylate copolymers, EPT, EPDM, etc. The polystyrene resin includes general grade polystyrene resin as well as α-methylstyrene copolymer.

Heat-resistant polystyrene resins such as styrene-maleic anhydride copolymers, styrene-alkylmaleimide copolymers, styrene-methyl methacrylate copolymers, and mixtures of polystyrene and polyphenylene oxide are used.

In addition, for the foam layer, it is recommended to use a mixed resin that is mainly composed of polyolefin resin and mixed with polystyrene resin because it has good rigidity and foamability.
preferable.

The foaming agent used in the foam layer may be any foaming agent that is normally used as a foaming agent for this type of foam.
For example, propane, butane, freon, etc.

Compounding agents such as stabilizers and fillers, which are common additives for thermoplastic resins, can be appropriately blended into the foam layer and the film layer.

The foam layer at the center of the laminated sheet has an expansion ratio of 1.2 to 5.5 times, and an expansion ratio of at least 1.2 is required to perform secondary foaming of the foam layer with vacuum on both sides. . On the other hand, a foamed sheet having a foaming ratio of 5.5 times or more is expensive to transport.

This is unfavorable from the viewpoint of productivity, and if the foaming ratio of the central foam layer is too high, peeling from the surface sheet layer is likely to occur. Considering these points, the foaming ratio of the foaming layer is 5.5. The following are suitable:

Next, the heating means will be described.

First, the above laminated sheet is heated and softened in a heating oven. At this time, the heating temperature is in the range of 110 to 190°C, and if it is below 110°C, sufficient vacuum foaming cannot be obtained. That is, it must be in a sufficiently softened state to be suctioned and foamed under vacuum pressure.

Therefore, it is heated to a temperature of 110° C. or higher, which is higher than the softening temperature of the resin. However, when heated to a temperature of 190℃ or higher,
Before vacuum foaming, the air layer within the laminated sheet is destroyed and becomes a non-foamed state, making vacuum foaming impossible.

By this heating, the laminated sheet usually undergoes some secondary foaming, and the laminated sheet becomes a secondary foamed laminated sheet having a lower density. There are also laminated sheets that do not undergo secondary foaming due to this heat softening.

Subsequently, the laminated sheet softened by heating is inserted between heated hot plates. That is, the laminated sheet is foamed and heated from both sides by a heated hot plate. On this occasion,
The hot plates used are two concave hot plates with vacuum suction holes. The clearance between the two plates is adjusted to be 1.2 to 5.5 times the thickness of the softened laminated sheet. in this case.

Since the laminated sheet is foamed with a clearance, the clearance affects the strength of the molded product after secondary foaming, and is 5.5
If the ratio exceeds 1.0 times, the secondary expansion ratio of the foamed layer due to this foaming heating will increase, and the strength of the resulting molded product will decrease.
If it is less than 3 times, foaming becomes meaningless.

The temperature of the hot plate is a temperature at which the secondary foamed laminated sheet can be molded, and is usually in the temperature range of 140-165°C, which is the temperature at which a molded article is formed from the laminated sheet. A primary foamed laminated sheet with a low density is inserted between the heating plates adjusted to the above heating temperature and clearance, the outer periphery of the laminated sheet is sandwiched, the air between the hot plates is exhausted, the pressure is reduced, and the laminated sheet is Foam and heat. In this case, foaming and heating is performed until the film of the laminated sheet comes into close contact with the hot plate.

The resulting foamed heated laminate sheet is then transferred to a forming means. As a means of forming.

Compression molding, vacuum molding, or other methods of folding may be employed.

The heating method of the present invention will be explained with reference to the drawings.

FIG. 1 shows the heating process of the present invention.

First, a three-layer laminated sheet 1, which is a raw sheet, is preheated in a heating oven 2 so that the raw sheet exhibits softening and plasticity. Next, the process moves to the foaming heating section 3, which is the heating means according to the present invention. This heating means consists of two heating plates 4 and 5 having vacuum holes. 1. The heating plates 4 and 5 are preheated as described above to sandwich the periphery of the laminated sheet having softened plasticity, and the clearance between the heating plates is softened.
It was set as 5 to 5.0 times. The raw sheet that has been foamed and heated by both heating plates is transferred to a molding section, where it is molded into a molded product.

EXAMPLE A sheet obtained by laminating a polystyrene foam layer of 875 microns with a foaming ratio of 2.25 times and a polystyrene film layer of 80 microns on the top surface and 55 microns on the bottom surface was used as a raw sheet (total thickness 1010 microns).

First, the original fabric sheet was preheated for 22 seconds using a far infrared heater at 250°C to bring the temperature of the original fabric sheet to 130-140°C.
℃.

Subsequently, the heating method according to the present invention is applied. The two upper and lower heating plates used were set at 157°C.

The preheated raw sheet is sandwiched between the heating plates. The clearance between the heating plates was 4.5 .mu.m/m, and the space surrounded by the heating plates was depressurized at 500 m/dg for 2.5 seconds. The sandwiched original fabric sheet was foamed, and the upper and lower film layers of the original fabric sheet were in close contact with their respective heating plates. then 1
．． After opening the inside of the heating plate to normal pressure for 5 seconds, the foamed original fabric sheet was held and moved to the molding section. The thickness of the foamed raw sheet at this time was 4.8 m/m.

In the molding section, the size of the molded product is 150+m/s x 15
0m/a, depth 25m/+s.

The temperature of the mold used was 24°C. The molding method was concave vacuum forming using the plug assist method, and the thickness of the resulting molded product on the side was 3.2+++/
The foaming ratio was 4.1 m/m at the bottom, and the foaming ratio of the part of the bottom that was hardly stretched was about 10 times.

Further, a good molded product was obtained without any problems such as separation from the mold.

(Effects) By employing the above-described configuration, the present invention can achieve the following effects.

1. By foaming and heating the original fabric sheet in a heated and softened state under vacuum before molding, a molded article with higher foaming can be obtained than with a low-foaming original fabric.

It is easier to obtain more uniform sheet heating temperature and uniform secondary foaming thickness between the two heating plates. As a result, the cells of the inexpensive molded article that has been subjected to secondary foaming are uniform.

The original fabric sheet made of three materials has a foam layer at its center and non-foaming film layers are laminated on both sides, so it not only allows vacuum forming even if one foam cell structure is connected. Since the foam layer has sufficient strength in the thickness direction to withstand the pressure difference in the temporary reduced pressure state of the foam layer until after foaming and molding, the decrease in thickness is small.

4 The foaming ratio is 1.5 of the initial original fabric sheet ratio for the molded product.
~5.0 times.

5. The mold temperature during molding is low, so the molding cycle is fast.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the steps of a method for thermoforming a thermoplastic laminate sheet according to the present invention. 1 Raw sheet 2 Heating oven 3 Foaming heating section 4, 5 Heating plate 6 Molding section 7 Molded product applicant Sekisui Plastics Co., Ltd.

Claims (1)

[Claims] 1. After heating and softening a thermoplastic laminate sheet having a three-layer structure consisting of a foam layer with an expansion ratio of 1.2 to 5.5 times and non-foaming films laminated on both sides of the foam layer at 110 to 190°C, It is inserted between hot plates whose clearance is adjusted to 1.5 to 5.0 times the thickness of the softened thermoplastic laminated sheet, and the peripheral edge of the thermoplastic laminated sheet is sealed and clamped, and the gap between the hot plates is After the air inside is evacuated and the pressure is reduced to foam the foam layer, and the double-sided film layer of the thermoplastic laminate sheet is heated so as to be in close contact with each hot plate, the thermoplastic laminate is heated between the hot plates. 1. A method for thermoforming a thermoplastic laminate sheet, which comprises taking out a sheet and forming it into a molded article having a desired shape.