Method for producing foam panels for the production of foam films

Abstract

The present invention relates to a method for producing a cellulose membrane having an average cell diameter of 20 μm to 250 μm, measured according to the standard ASTM D 3576, and having a cell diameter of >260 μm per 1 m. 2 and a glass transition temperature T of at least 100°C, characterized in that there are fewer than 20 particles per 100°C, and the foam has an elongation at break of 4% to 13%, as measured in accordance with ASTM D 638. g The present invention relates to a method for producing a foam panel for use in producing a foam film made of a polymer having the formula:

Description

[Technical field]

[0001] The present invention relates to a method for producing a cellular membrane having an average cell diameter of 20 μm to 250 μm, measured according to the standard ASTM D 3576, and having cells with a diameter >260 μm within 1 m. 2 and the foam has a glass transition temperature T of at least 100° C., characterized in that there are fewer than 20 per one particle and the foam has a breaking elongation of 4% to 13%, as measured according to ASTM D 638. g The present invention relates to a method for producing a foam panel for use in the production of a foam film made of a polymer having the formula:

[0002] Prior Art Rigid foam, e.g. product name Rohacell (登録商標) Polymethacrylimide, available commercially from Rohacell, can be cut in a variety of ways, just like other foams. (登録商標)The standard method of cutting in this case is by sawing. This involves the horizontal division of the thick foam block with a band saw, which generates a considerable amount of saw dust. Moreover, it is almost impossible to obtain thin or very thin sheets or films from the rigid foam by this method. Very thin films are not achievable otherwise due to the thickness of the saw blade and the relatively high mechanical stresses in the areas of the rigid foam that can be cut in the course of sawing. And also thin sheets with a thickness of 3-10 mm are only possible with high material losses and considerable dust formation, since the saw blades used in sawing have a considerable thickness of at least 2 mm, which results in corresponding material losses. And also, if the saw blade is particularly thin, it will sag and lead to large thickness differences in the cut product and / or make cutting of the film virtually impossible. If thicker sheets having a thickness of more than 10 mm are to be divided, problems also arise during the sawing process, since the bending of the area to be cut caused by the thickness of the saw blade may lead to its destruction during the division. This is a problem that occurs especially in the case of very hard and therefore somewhat brittle foams.

[0003] Flexible foams, for example flexible polyurethane foams, can also be cut by using a band knife without producing sawdust as waste. Many foams (rigid and flexible) can additionally be cut using a heated tension wire. However, here thermal damage of the material is possible as a result of said hot wire. Furthermore, here there is also the problem of material loss or destruction of thin sheets as a result of the finite thickness of the wire.

[0004] A method for planar splitting of rigid foams, suitable for obtaining films or thin sheets, is described in US 10,556,357. This method is characterized in that the rigid foam is first softened and then cut with a knife. The foam films described in this intellectual property show insufficient elongation at break due to a large number of pinholes.

[0005] assignment Thus, against the background of the reviewed prior art, the problem addressed by the present invention is a method for producing a foam panel from which a foam having a glass transition temperature T of at least 100° C., with small cell diameters and few pinholes, is obtained. g The object of the present invention is to provide a method which makes it possible to provide a polymeric thin foam film having a The method for producing the foam panels shall be particularly suitable for producing foam films from these foam panels having a thickness of less than 3 mm. The division of the foam panels shall be carried out without the formation of chips.

[0006] Other issues not explicitly discussed herein may be derived from the prior art, the specification, the claims, or the exemplary embodiments.

[0007] solution The objective is to obtain a glass transition temperature T g , with an average cell diameter of 20 μm to 250 μm and a 1 m 2 1. A method for producing a foam panel for the production of a foam film consisting of a polymer having less than 20 cells with a diameter >260 μm per cell and an elongation at break of the foam panel of 4% to 13%, measured according to ASTM D 638, comprising: A) removing the foam skin of the foam block; and B) Cut the remaining part of the foam block into foam panels having a thickness of 10 to 135 mm. The problem has been solved by providing a method, characterized in that

[0008] The foam panels according to the invention have a glass transition temperature T of at least 100° C., preferably at least 140° C., measured according to DIN EN ISO 11357-2. g The standard DIN EN ISO 11357-2 for plastics (published July 2014) describes Differential Scanning Calorimetry (DSC) - Part 2: Determination of glass transition temperature and glass transition activation energy.

[0009] The polymer is selected from the group consisting of polyethersulfone, polyphenylsulfone, polyetheretherketone, poly(meth)acrylimide, polymethyl(meth)acrylate, polyetherimide, polysulfone, polyurethane, polyethylene terephthalate, and mixtures and copolymers thereof. The term poly(meth)acrylimide (P(M)I) should be understood below as meaning polymethacrylimide (PMI), polyacrylimide (PI) or mixtures thereof. The same applies, for example, to polymethyl(meth)acrylate. Correspondingly, the term polymethyl(meth)acrylate should be understood as meaning not only polymethylmethacrylate, but also polymethylacrylate and mixtures thereof. The material for the foam core is preferably P(M)I, particularly preferably PMI. Such P(M)I foams are also called rigid foams and exhibit particular strength. The production of P(M)I foams is described, for example, in EP 3221101. The P(M)I foams are usually produced in a two-stage process: a) the production of a casting polymer and b) the foaming of this casting polymer. The casting polymer is produced by first preparing a monomer mixture containing as main components (meth)acrylic acid and (meth)acrylonitrile, preferably in a molar ratio of 2:3 to 3:2. In addition, it is possible to use further comonomers, such as esters of acrylic or methacrylic acid, styrene, maleic or itaconic acid or their anhydrides or vinylpyrrolidone. However, the proportion of said comonomers should not exceed 30% by weight. It is also possible to use small amounts of crosslinking monomers, such as allyl acrylate. However, said amount should preferably be at most 0.05 to 2.0% by weight.

[0010] The copolymerization mixture further contains a blowing agent which decomposes or evaporates to form a gas phase at a temperature of about 150° C. to 250° C. Since the polymerization is below this temperature, the casting polymer contains a latent blowing agent. The polymerization is advantageously carried out in the form of a block between two glass plates. For the production of foam sheets, this is followed by foaming the casting polymer at a suitable temperature in a second step according to the prior art. The production of these P(M)I foams is in principle known to the skilled artisan and can be found by way of example in EP 1 444 293, EP 1 678 244 or WO 2011 / 138060. Examples of PMI foams are in particular the ROHACELL foams from Evonik Industries AG, Germany. (登録商標) Acrylimide foams can be considered similar to the PMI foams in terms of manufacture and processing, however, for toxicological reasons they are substantially less preferred compared to other foam materials.

[0011] The density of the rigid foam material can be selected relatively freely. P(M)I foams have a density of, for example, 20 to 320 kg / m 3 , preferably 25 to 250 kg / m 3 It may be used in the density range of 30 to 200 kg / m 3It is particularly preferred to use a PMI foam having a density of

[0012] The foams described herein are produced in foam blocks that have a variety of thicknesses according to the polymer used and the density achieved.

[0013] It has been found to be particularly advantageous to use only foam from specific areas of the foam block. It has been found that removing the foam skin / surface of the foam block results in a foam panel with very good mechanical properties.

[0014] It is preferred if 3 mm, particularly preferably 5 mm, very particularly preferably 10 mm and especially preferably 15 mm of the surface / foam skin of the foam block is removed, the remaining material having a better homogeneity of cell size and elongation at break and therefore suitability for processing into foam panels.

[0015] The remaining part of the foam block is cut into foam panels having a thickness of 10-135 mm, preferably 60-125 mm, particularly preferably 75 mm.

[0016] Various methods are known for cutting foam panels from foam blocks. The cuts are preferably made using a laser, a band knife or a band saw.

[0017] The foam panels produced according to the invention are particularly suitable for producing foam films.

[0018] The foam panels can be used to produce foam films of particularly low thickness. Thin foam films having a thickness of 0.05 to 3 mm can be produced. It is preferred to obtain foam film thicknesses of 0.15 to 1 mm.

[0019] A particular problem in the production of foam films is pinholes. In this context, the term pinholes refers to relatively large cells that form on the surface of the film and cause a reduction in strength. In extreme cases, the cell size is larger than the thickness of the film, so that holes form in the film.

[0020] According to the invention, the foam film has an average cell diameter of the foam of 20 μm to 250 μm, preferably 50 μm to 220 μm, particularly preferably 80 to 200 μm, measured according to standard ASTM D 3576. Standard ASTM D 3576 (2015 edition) is used to determine the cell size of rigid foams.

[0021] To obtain the desired mechanical properties, especially the elongation at break, cells with a diameter >260 μm are used for 1 m 2 There are fewer than 20 cells per square meter with a cell diameter >260 μm. 2 It is preferred that there are fewer than 15 per molecule.

[0022] Preferred are foam films having an elongation at break of 4% to 30%, particularly preferably 5% to 10%, measured according to ASTM D 638 (2014 edition), which corresponds to ISO 527-1 and is a standard test method for determining the tensile properties of plastics.

[0023] In particular, particularly rigid foams having high stiffness and brittleness, such as rigid P(M)I foams, can suffer from problems with their slabs breaking during the cutting process, especially as a result of the wedge-shaped cross-section of the blade.

[0024] Foams with special properties, such as high breaking elongation and cell structure, are suitable for splitting into thin layers. Splitting of rigid foams is a very efficient method for producing thin layers, for example those used in speakers for smartphones. Due to the mechanical requirements of the splitting method (deflection of the cut film at the cutter bar), a high breaking elongation of the foam is advantageous for the process stability and the layer thickness that can be achieved. The cut foam film is adhesively bonded to a very thin layer of aluminum foil, through which relatively coarse and inhomogeneous cells can become visible, so a cell structure as fine and homogeneous as possible is required.

[0025] In one variant of the process, the division of the still-heated rigid foam is carried out immediately after the foaming operation in an oven or hot press. There are also various embodiments regarding the arrangement of the knives.

[0026] In a preferred embodiment, the rigid foam slab is moved perpendicular to the cutting surface of the knife, while the knife moves only perpendicular to the transport direction of the rigid foam slab. Alternatively, but less preferably, the knife in the cutting operation is moved along the fixed rigid foam. It is also possible for the knife and the rigid foam to have opposite directions of movement, in which case the knife in the latter two variants can effectively move perpendicular to the rigid foam in addition to supporting the cutting operation. In the case of the movement of the knife at a right angle, there are again two variants. Firstly, the knife can move back and forth. However, it is preferred to use a band knife. Such a band knife is moved in one direction, once around, at a right angle to the cutting direction, and is generally guided and driven by at least two guide rollers. Band knife systems are commercially available.

[0027] In a particular embodiment, several pieces, for example in the form of films or thin sheets, are cut from the rigid foam in one movement by several knives arranged in series. These may in particular be several band knives arranged in series, thus making it possible to cut several workpieces from one block in one operation in a very efficient manner.

[0028] Alternatively or additionally, the film can be subsequently covered with at least one outer layer. These outer layers can be, for example, composite material, metal or wood. This makes it possible to realize sandwich materials, for example, for use in lightweight construction. Alternatively, the outer layer can simply be a protective film or a decorative layer that can simply be removed again. In particular, the application of very thin aluminum foil is important.

[0029] The great advantage of the present invention is that the generation of waste in the form of sawdust during cutting of the rigid foam is virtually avoided and thermal damage of the rigid foam surface is eliminated, which makes it possible to limit material losses and the process is entirely more economical than the prior art processes.

[0030] In principle, the thin foam films described above have a very wide range of applications. They can be used, for example, as membranes, especially in speakers, mobile music players or headphones. Their use for decorative purposes, for example for the surface finishing of articles, is also conceivable.

Claims

1. A glass transition temperature T of at least 100° C. ｇ , an average cell diameter of 20 μm to 250 μm, measured according to standard ASTM D 3576, and ２ 1. A method for producing a foam panel for the production of a foam film consisting of a polymer having less than 20 cells with a diameter greater than 260 μm per cell and an elongation at break of the foam panel of 4% to 13% as measured according to ASTM D 638, comprising the steps of: A) removing the foam skin of the foam block; and B) Cut the remaining part of the foam block into foam panels having a thickness of 60-135 mm. The method according to claim 1,

2. The method of claim 1 , wherein the polymer has a glass transition temperature of at least 140° C.

3. 3. The method of claim 1 or 2, wherein the polymer is selected from the group consisting of polyethersulfone, polyphenylsulfone, polyetheretherketone, poly(meth)acrylimide, polymethyl(meth)acrylate, polyetherimide, polysulfone, polyurethane, polyethylene terephthalate, and mixtures and copolymers thereof.

4. The method according to any one of claims 1 to 3, wherein the foam panel has an average cell diameter of from 50 μm to 220 μm, preferably from 80 μm to 200 μm.

5. The cells having a cell diameter of more than 260 μm are ２ 5. The method of claim 1 , wherein there are less than 15 per nucleotide.

6. 6. The method of any one of claims 1 to 5, wherein the foam panel has an elongation at break, measured according to ASTM D 638, of 5% to 10%.

7. 7. The method according to claim 1, wherein in step A) the foam skin of the foam block has a thickness of 3 mm.

8. 8. The method according to claim 1, wherein in step B) the foam panel is cut using a band knife or a band saw.