JPH0798351B2 - Method for manufacturing laminated foam sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foamed sheet of a polyolefin resin.
More specifically, the present invention relates to a method for producing a foamed sheet made of a polyolefin resin having excellent heat insulating properties, cushioning properties, strengths, thermoformability, adhesive properties, surface smoothness and the like.

The foamed sheet produced by the method of the present invention can be used for internal parts of automobiles, box-shaped heat insulating materials such as ice boxes, cushioning materials, and containers such as food containers.

[Conventional technology]

Foamed sheets of polyolefin resin have hitherto been used in various fields, and the following methods (a) to (c) are known as manufacturing methods thereof.

(A) A composition obtained by adding a substance (foaming agent) that thermally decomposes to generate gas to a polyolefin resin is extruded using an extruder while melt-kneading at a temperature equal to or higher than the temperature at which the foaming agent decomposes. How to make a single layer foam sheet. This method is suitable for producing a low expansion ratio product having an expansion ratio of about 1.5 times or less, but as the expansion ratio is increased, the surface of the sheet becomes extremely rough and loses practical value. It should be noted that the low expansion ratio product has a problem that the effects such as heat insulating property, cushioning property, and lightness due to foaming cannot be sufficiently exhibited.

(B) A method for producing a foamed sheet by melt-kneading a polyolefin resin while extruding it as a single layer while injecting a gas or a highly volatile liquid from the cylinder portion of an extruder. This method can be applied to the production of foamed sheets with low to high expansion ratios, but it is difficult to control the bubbles, and it is necessary to use specially blended raw materials with extremely high viscosity in order to make good foamed sheets. There is such a problem.

(C) A polyolefin resin is mixed with a foaming agent and a crosslinking aid such as divinylbenzene, and the composition is molded at a temperature at which the foaming agent does not decompose into a sheet, and then the sheet is irradiated with an electron beam or the like. A method of producing a single-layer foamed sheet by causing a crosslinking reaction to crosslink, and then heating the sheet to a temperature at which the foaming agent decomposes or higher to foam. This method is also applicable to the production of foamed sheets with low expansion ratio to high expansion ratio, but the manufacturing process is complicated, there are many restrictions on the raw materials that can be used, and the control of the crosslinking reaction and subsequent expansion is severe, so product quality is high. There is a problem with stability and the product becomes very expensive.

In addition to these problems, all of the products obtained by the conventional manufacturing method are not a sufficient adhesiveness because they are a single layer product of polyolefin, and the sheet surface does not have a high-strength unfoamed layer, which is strong. When a compressive force is applied, the bubbles are crushed and the gas easily escapes, which is another drawback.

[Problems to be solved by the invention]

Polyolefin resin foamed sheets are extremely useful industrially, but conventional manufacturing techniques and their products cannot produce high-quality foamed sheets with good surface properties (a) as described above.
(B) Difficult to control air bubbles, (c) Insufficient quality stability and expensive products, (d) Weak in compression force, (e)
There were problems such as insufficient adhesion. The purpose of the present invention is to
To improve these problems, the expansion ratio is about 2 to 25 times,
It is intended to provide a method for producing a foamed sheet of a polyolefin resin having a thickness of about 1 to 5 mm.

[Means for solving problems]

In order to achieve the above object, the present invention has the following configuration. That is, (1) a polyamide resin, a modified polyolefin resin, a polyolefin resin containing a foaming agent, a modified polyolefin resin and a polyamide resin are sequentially laminated by a coextrusion method at a temperature below the decomposition temperature of the foaming agent. A method for producing a laminated foam sheet, which comprises extruding a laminated non-foamed sheet, heating the sheet to a temperature not lower than the decomposition temperature of a foaming agent to foam, and then cooling while suppressing the foaming agent on both sides.

(2) The production method according to (1) above, wherein the decomposition temperature of the foaming agent is 30 to 75 ° C. higher than the melting point of the polyolefin resin.

(3) The production method according to the item (1), wherein the melting point of the polyamide-based resin is equal to or higher than the decomposition temperature of the foaming agent.

In the present invention, the polyolefin resin is a crystalline polypropylene homopolymer, a copolymer of crystalline propylene and a comonomer other than propylene, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density. Examples thereof include polyethylene, ultra-low density polyethylene, ethylene vinyl acetate copolymer and the like. There is no particular limitation on the melt index measured by the JIS method (K6760 for polyethylene, K6758 for polypropylene), but 0.5 to 5 g / in terms of extrusion processability, uniformity of foaming, etc.
10 mm is preferred. One or more of the above polyolefin resins may be mixed and used.

The modified polyolefin resin is obtained by graft-polymerizing one or more polymerizable monomers selected from polymerizable unsaturated carboxylic acids, salts of polymerizable unsaturated carboxylic acids, esters and amides onto the polyolefin resin. To be Examples of the polymerizable monomer include acrylic acid, methacrylic acid,
Maleic anhydride or an ester or amide thereof may be used alone or as a mixture, and as the polyolefin to be grafted, polyethylene or polypropylene may be mentioned.
The modified polyolefin resin is a method in which a polyolefin resin and a polymerizable monomer are dissolved and heated in a solvent such as toluene or xylene in the presence of an organic peroxide to perform graft polymerization, and the polyolefin resin and the polymerizable monomer are ion-irradiated. Can be prepared by a method of contacting under irradiation of, a method of melting and kneading a mixture of a polyolefin resin, a polymerizable monomer and a radical initiator with an extruder or a kneader, and the product thus obtained is Mitsui Sekiyu. Examples include Admer manufactured by Kagaku Kogyo Co., Ltd. and Model manufactured by Mitsubishi Petrochemical Co., Ltd.

If the polyamide resin layer and the polyolefin resin layer containing the foaming agent are not sufficiently adhered, the generated gas cannot be contained in the laminated sheet when heated and foamed, so that not only a highly foamed sheet cannot be obtained. The surface of the foam sheet becomes rough and loses its practicality. Since polyamide and polyolefin are not welded, a modified polyolefin resin is used to weld and integrate them. The melting point is preferably as close as possible to that of the polyolefin resin used. Further, the modified polyolefin resin may be used by appropriately blending a polyolefin resin or a polyamide resin.

As the polyamide-based resin, a ring-opening polymer of ε-caprolactam (nylon 6), a condensation polymer of hexamethylenediamine / adipic acid (nylon 66), a condensation polymer of hexamethylenediamine / sebacic acid (nylon 610), 11 Examples thereof include condensation polymerization products of aminoundecanoic acid (nylon 11) and ring-opening polymerization products of ω-laurolactam (nylon 12). The melting point of the polyamide resin needs to be equal to or higher than the decomposition temperature of the foaming agent. Below the decomposition temperature,
When the laminated sheet is heated to foam the polyolefin resin layer, the melt viscosity of the polyamide resin layer becomes insufficient, the generated gas cannot be contained in the polyolefin resin layer, and the heated foam sheet becomes difficult to transfer. A small amount of a polyolefin resin or a modified polyolefin resin may be blended with the polyamide resin.

The melting point referred to in the present invention is a melting point (melting peak) determined by DCS (differential scanning calorimeter). Depending on the product, the melting peak is not limited to one, but the melting point in this case has the maximum peak and is the melting point of the product.

As a foaming agent, azodicarbonamide, azobis isobutyronitrile, barium azodicarboxylate,
Azo compounds such as azocyclohexyl nitrile, benzenesulfonyl hydrazide, P, P'-oxy-bis (benzenesulfonyl hydrazide), para-toluene sulfonyl azide, sulfonyl hydrazide compounds such as trihydrazino triazine, dinitroso pentamethylene・
Examples thereof include nitroso compounds such as tetramine, N, N ′ dinitroso N, N ′ dimethyl terephthalamide, and mixtures of carbonates and organic acids (Daiflow Seika Kogyo Co., Ltd., Daiflow 1003, etc.). These foaming agents can be used as a mixture of one or more kinds. Their decomposition temperature must be 30 to 75 ° C higher than the melting point of the polyolefin resin.
When the height is less than 30 ° C, there is a disadvantage that a part of the foaming agent is foamed due to shearing heat generation or the like at the stage of manufacturing the laminated unfoamed sheet, and when the height is more than 75 ° C. Requires a higher temperature in the step of heat-foaming the laminated unfoamed sheet, so that the melt viscosity of the foaming-treated sheet becomes too low and it becomes difficult to transfer, and a laminated foamed sheet having a uniform and excellent appearance is obtained. There is a problem that you can not get it.

The laminated unfoamed sheet is produced by the coextrusion method, but either the multi-manifold method or the feed block method can be used. Although the thickness constitution of the laminated unfoamed sheet is not particularly limited, 20 to 50 μm is sufficient for the modified polyolefin resin layer, and 50 to 200 μm is suitable for the polyamide resin layer.

The laminated unfoamed sheet is heated in a temperature range not lower than the decomposition temperature of the foaming agent used and not higher than the melting point of the polyamide resin used to foam the polyolefin resin layer. This heating is a method of contacting the laminated unfoamed sheet with a heated roll,
It is preferably carried out by a method of heating with a heating open, a method of contacting with a heating plate, a method of immersing a heating liquid in a bath or a method of combining these. The heating temperature is a temperature higher than the decomposition temperature of the foaming agent and lower than the melting point of the polyamide-based resin used, but it takes about 10 ° C. above the decomposition temperature because it takes a long time to obtain sufficient foaming in the vicinity of the decomposition temperature of the foaming agent. The higher temperature is preferable. If the temperature is higher than the melting point of the polyamide-based resin used, air bubbles cannot be contained in the polyolefin-based resin layer, and it becomes difficult to transfer the foam-treated sheet, which is not preferable. At this time, even if the foamed sheet is forcibly transferred to the cooling step, a good product cannot be obtained.

The foamed sheet obtained in the heating step is cooled in the last step. Cooling is a method of passing between paired cooling rolls,
It is preferably carried out by a method of passing it between a pair of cooled steel belts, and the cooling temperature at that time is preferably 40 ° C. or lower.

In one embodiment of the present invention, an adhesive agent such as fluid paraffin is added to a polyolefin resin layer constituting a laminated unfoamed sheet,
Antioxidants, dispersants, foaming aids, antistatic agents, UV absorbers, metal resistant agents, coloring agents, fillers such as calcium carbonate and talc, synthetic rubber and various thermoplastic resins, maleic anhydride and acrylic acid. The addition of components such as the thermoplastic resin modified by the method can be arbitrarily performed as necessary.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. The properties of the polyolefin resin, the modified polyolefin resin, the polyamide resin and the foaming agent used in each example are summarized in Table 1. The melting point of each resin is DS
The main peak of the melting point obtained by C (Differential Scanning Calorimeter) is shown, and the melting index for polypropylene is
For JIS K6758 and for polyethylene, the values are obtained according to JIS K6760.

In addition, the laminated unfoamed sheet, the foamed treated sheet and the laminated foamed sheet obtained by each treatment process are evaluated according to the following criteria for the state, transportability and surface smoothness, and adhesion of the polyolefin resin layer to other layers. did.

Example 1 Preparation of laminated unfoamed sheet: See Table 1 for polyolefin resin (hereinafter sometimes referred to as PO resin).
XK0235 is used, and liquid paraffin is used as an adhesive.
An example in which 0.3 PHR was added, the mixture was mixed for 3 minutes with a high-speed rotary mixer (Hensiel mixer), and then Sermic C (see Table 1) was added as a foaming agent. Extruder has one 65mmφ and 40
Using a multi-manifold type co-extrusion device having two mmφ, the mixed composition of the PO-based resin and the foaming agent obtained as described above is converted into a modified polyolefin resin (hereinafter referred to as modified PO-based resin) from a 65 mmφ extruder. LB310
40 mm each (see Table 1) and CM1041 (see Table 1), which is a polyamide resin (hereinafter sometimes referred to as PA resin).
Extruded from a φ extruder to make an unfoamed laminated sheet. The thickness and extrusion temperature at that time are as shown in Table 2. In addition,
There are two modified PO-based resin layers and two PA-based resin layers on the upper and lower sides.

Foaming treatment: 30x the laminated unfoamed sheet obtained above
It was cut into a size of 30 cm, and a far-infrared heater was installed on the top, and it was placed in a silicone oil tank heated by an electric heater from the inside of the tank and heated at 220 ° C. for 5 hours to foam. The resulting foamed sheet is taken out from the silicone oil tank by sandwiching one side with a take-out tool having three-point nipping parts, and then placed on a stainless steel plate (cooling plate) having a thickness of 5 mm and a size of 40 × 50 cm. Transferred.

Cooling treatment: The foamed sheet transferred onto the stainless steel plate was quickly moved to a press machine together with the stainless steel plate, and cooled while being pressed from both sides with the press. As the above-mentioned pressing machine, a stainless steel plate is attached to the bolster on the side opposite to the stainless steel plate on which the foamed sheet is placed.This stainless steel plate has a clearance (clearance) for maintaining a constant thickness even when the foamed sheet is pressed. (Adjustment) Jig is attached,
The bolster of the press was equipped with a means for passing cooling water. Cooling: clearance between cooling plates: 5.0 mm, temperature: 3
The test was performed at 0 ° C., time: 5 minutes, and pressing force: 2 kg / cm ² .

The laminated foamed sheet thus obtained had a thickness of 5.0 mm and a foaming ratio of 9.5 times, and the surface smoothness and the adhesion to other layers of the PO-based resin layer were good as shown in Table 2.
Although Table 2 also shows the state of the laminated unfoamed sheet and the evaluation of the transferability of the foamed sheet,
All are known to be good.

Examples 2 to 15 The laminated foamed sheets were manufactured and evaluated in the same manner as in Example 1 except that the manufacturing conditions were changed variously within the scope of the present invention. The results are shown in Table 2.
It was shown to.

Comparative Examples 1 to 7 Sheets obtained by manufacturing and processing steps of laminated sheets were evaluated in the same manner as in Example 1 except that manufacturing conditions outside the scope of the present invention were included. The results are shown in Table 3.

As is clear from Table 2 and Table 3, Examples 1 to 3 are examples in which polypropylenes having mutually different properties are used as PO-based resins, and Examples 4 to 5 are Examples 2-3 in which polyethylene-based resins are used. It is an example in which a foamed sheet is prepared under the same conditions as in Example 1, but it can be seen that a good foamed sheet is obtained in each case. Examples 6 to 7 are the same as Example 2 except that the amount of the foaming agent was changed. However, even if the amount of the foaming agent was changed, good foamed sheets can be obtained. Example 8 is an example in which low-density polyethylene having a low melting point is used as the PO-based resin, and the blowing agent and the PA-based resin are also within the scope of the present invention, and Example 9 is a combination of two types of the blowing agents. In the same manner as in Example 8, except that the PA resin was different, a good foamed sheet can be obtained. Example 10 is an example performed in the same manner as in Example 2 except that the PO-based resin is a mixture of polypropylene and polyethylene, and Examples 11 to 12 are similar to Example 2 except that the modified PO-based resin is changed. In the implemented example,
In each case, a foamed sheet having no problem was obtained. Example
Nos. 13 to 15 are examples carried out in the same manner as in Example 2 except that the thickness of each layer constituting the laminated unfoamed sheet was changed. From these examples, a good foamed sheet can be obtained even if the thickness of each layer is different. Is known. From each of the above examples,
It can be seen that a good laminated foam sheet can be obtained under the conditions satisfying the present invention.

On the other hand, in the comparative examples including the conditions that do not satisfy the present invention, good foamed sheets cannot be obtained. That is, when the decomposition temperature of the foaming agent is less than the melting point of the PO-based resin + 30 ° C., and when the composition is extruded at a temperature equal to or higher than the decomposition temperature of the foaming agent, PO
In Comparative Example 7 in which the sheet of the resin layer is formed, a good laminated foamed sheet cannot be obtained because foaming occurs in the stage of forming the laminated unfoamed sheet. In Comparative Example 2 in which the PA-based resin having a melting point lower than the decomposition temperature of the foaming agent was used, when the laminated unfoamed sheet was foamed, the viscosity of the PA-based resin layer was significantly decreased, resulting in poor transportability and good lamination. Foam sheet cannot be obtained. Further, naturally, in Comparative Example 3 in which the laminated unfoamed sheet is heated at a temperature equal to or lower than the decomposition temperature of the foaming agent, no foaming occurs. In Comparative Example 4 without the modified PO-based resin layer and the PA-based resin layer, a good foamed sheet cannot be obtained due to problems in transportability. In Comparative Example 5 without the modified PO resin layer, the PO
The adhesiveness between the PA resin layer and the PA resin layer is poor, and a good laminated foam sheet cannot be obtained. In Comparative Example 6 in which the foamed sheet is cooled from both sides without being suppressed, there is a problem that large irregularities occur on the surface of the product.

〔The invention's effect〕

As explained above, according to the present invention, there is no unevenness on the surface,
In addition, a laminated foam sheet having a polyolefin resin layer from low foaming to high foaming in the center can be easily prepared. Further, since the laminated foam sheet has a polyamide resin layer on the surface layer, it has improved adhesiveness and printability, which are drawbacks of the polyolefin resin, and is thus suitable as a material for automobile interior parts and food containers. It will be

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Claims (3)

[Claims] 1. A polyamide resin, a modified polyolefin resin, a polyolefin resin containing a foaming agent, a modified polyolefin resin and a polyamide resin are sequentially laminated by a coextrusion method at a temperature below the decomposition temperature of the foaming agent. A method for producing a laminated foam sheet, which comprises extruding a laminated unfoamed sheet, heating the sheet to a temperature equal to or higher than the decomposition temperature of a foaming agent to foam, and then cooling while suppressing from both sides. 2. The production method according to claim 1, wherein the decomposition temperature of the foaming agent is 30 to 75 ° C. higher than the melting point of the polyolefin resin. 3. The manufacturing method according to claim 1, wherein the melting point of the polyamide resin is not lower than the decomposition temperature of the foaming agent.