BRUSH FILAMENTS PREPARED FROM A POLYTRIMETHYLENE TEREPHTHALATE COMPOSITION AND BRUSHES COMPRISING THE SAME

FIELD OF THE INVENTION

The present invention relates to a monofilament bristle, more specifically to a monofilament bristle made of polytrimethylene terephthalate composition. The invention also relates to a brush comprising the monofilament bristle.

BACKGROUND OF THE INVENTION

In the fields of toothbrushes, paint brushes, cosmetic brushes and so on, the monofilament bristles are usually made of chemically synthetic materials such as polybutylene terephthalate (PBT). Due to the inherent functional features of a toothbrush, there are some special requirements for choosing monofilament bristle materials used for toothbrushes. For example, polyamide 6,12 has been used in toothbrushes because it is soft when making contact, will not harm the teeth, and has good flexural recoverability. However, polyamide is highly hygroscopic; when it absorbs water, its physical properties and flexural recoverability decrease and its size changes significantly. Therefore, if the toothbrush is continually used for some time, the polyamide monofilament bristles spread open from each other, thus its durability decreases. Moreover, using polyamide costs more. In addition, due to polybutylene terephthalate (PBT)'s high hardness, poor tenacity, high brittleness and high rigidity, it cannot be used directly for making a toothbrush. In the industry, the tips of the

monofilament bristle made by polybutylene terephthalate are usually sharpened with a chemical flux etching technique, and softened before it is used for the toothbrush. This technique undoubtedly increases cost and causes problems such as environment pollution by chemical etching solutions.

Other polyester materials (such as polyethylene terephthalate (PET)) used to replace polyamide or polybutylene terephthalate to prepare monofilament bristle products have been investigated. For example, German patent application 19937729A1 discloses a high strength polyester yarn for industrial use, comprising polyethylene terephthalate and 0.1-2 wt.% of amorphous copolymer filler; Japanese patent application JP 2002020931 A discloses a polyester filament used in handmade paper or canvas strap, the polyester filament comprises polyethylene terephthalate, 1-15 wt.% of polyethylene-acrylate copolymers and 0.3-3.0 wt.% of carbodiimide; US patent application

20090075543A1 discloses a monofilament used in the textile or paper-making industries. The monofilament comprises a two-phase polymer blend, wherein the polyethylene terephthalate serves as the first phase, and ethylene copolymer serves as the second phase polymer.

Polytrimethylene terephthalate (PTT) is another type of high performance polymer in the field of polymeric synthetic material. It is a type of thermoplastic polyester with excellent performance, outstanding chemical resistance, elasticity, better dyeability and color fastness, as well as having advantages such as good stain resistance, resistance to ultra light, resistance to nitrogen oxides, resistance to ozone, and antistatic, etc. Moreover, because 1,3-propylene glycol, which is one of the starting materials used in the preparation of polytrimethylene terephthalate, can be obtained via a biochemical process, its application further gains extensive attention and investigation.

For example, US patent 6,673,444B2 discloses a monofilament form of a copolymer comprising more than 90 mol% of trimethylene terephthalate repeating units and less than 10 mol% of other polyester repeating units, wherein the substances that could form other polyester repeating units comprise polyethylene terephthalate, polyamide, or dicarboxylic acid and/ polyols. The

monofilament is excellent in softness, bending recovery and durability. The monofilament can be used to weave yarns or bristles.

The application of polytrimethylene terephthalate in the industry of monofilament bristles, especially in the industry of toothbrush bristles, has been disclosed as well, an example is US patent 6,053,734. Specifically, US patent 6,053,734 discloses a monofilament bristle made of

polytrimethylene terephthalate and a monofilament bristle with a core-sheath structure. The monofilament bristle with a core-sheath structure comprises a core formed by a polymer having high flexural elastic modulus, such as polyethylene terephthalate, and a sheath formed by

polytrimethylene terephthalate.

In addition, a Japanese patent application JP 2007-000519 also discloses a bristle and a toothbrush made with the bristle. The bristle possesses a core-sheath structure as well and comprises a core with two or more resin layers coating the core in the form of a concentric circle, wherein the core is made of polytrimethylene terephthalate (PTT), and the outer resin layer is made of polyester- based resin (such as Hytrel ^® copolyether-ester resin) other than polytrimethylene terephthalate (PTT), and an intermediate layer interposed between the core and the outer resin layer is made of a blend of polytrimethylene terephthalate and the above polyester-based resin other than

polytrimethylene terephthalate. The function of the intermediate resin layer is to provide adhesion between the core and the outer layer of the bristle.

Although in the prior art polytrimethylene terephthalate has been used for making the monofilament bristle, the inventors of this application have discovered that in terms of its applications in toothbrushes, paint brushes, cosmetic brushes or industrial brushes, the hardness of polytrimethylene terephthalate is still high, and because of its poor tenacity and high brittleness, it needs to be further modified in order to provide modified products with a simple process, low cost, and the ability to concurrently meet the demand of monofilament bristles with different physical properties in the production practice, resulting in polytrimethylene terephthalate compositions having characteristics such as softness, low elongation at break % and high flexural recoverability simultaneously. SUMMARY OF THE INVENTION

Disclosed herein is monofilament bristle made of a modified polytrimethylene terephthalate composition, wherein, based on the total weight of the modified polytrimethylene terephthalate composition, the modified polytrimethylene terephthalate composition comprises:

(a) 85-95 wt.% of at least a polytrimethylene terephthalate, and

(b) 5-15 wt.% of at least a poly ethylene -methyl acrylate copolymer;

and the modified polytrimethylene terephthalate composition has a flexural modulus of 2500MPa or lower measured according to ISO 178:2001, and a tensile modulus of 2600MPa or lower, and an elongation at break % of 20% or lower, measured respectively according to IS0527-2: 1993.

Also disclosed is a brush comprising the monofilament bristles described immediately herein above. DETAILED DESCRIPTION OF THE INVENTION

It should be pointed out that, in the present invention, when any value range provides specific values of the upper and lower endpoints, the range includes any value within the endpoints and the equal or almost equal values of the endpoints.

Unless otherwise stated, all publications, patent applications, patents and other references mentioned in this text are incorporated herein in their entirety by reference, as if presented in full text within this text.

Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those used by a person skilled in the art. In case of a conflict, the definitions in this specification shall govern.

Unless otherwise stated, all percents, parts, ratios, etc. are based on weight.

The present invention first discloses a monofilament bristle made of modified polytrimethylene terephthalate composition, wherein, based on the total weight of the modified polytrimethylene terephthalate composition, the modified polytrimethylene terephthalate composition comprises:

(a) about 85 to about 95 wt.% of polytrimethylene terephthalate (PTT), and

(b) about 5 to about 15 wt.% of at least a polyethylene-alkyl acrylate copolymer,

and the modified polytrimethylene terephthalate composition has a flexural modulus of 2500MPa or lower measured according to ISO 178:2001, and a tensile modulus of 2600MPa or lower, and an elongation at break % of 20%> or lower, measured respectively according to IS0527-2: 1993.

In one embodiment of the monofilament bristle, the modified polytrimethylene terephthalate composition is a single phase composition formed by at least a polytrimethylene terephthalate and at least a polyethylene-alkyl acrylate copolymer.

In another embodiment of the monofilament bristle, the modified polytrimethylene terephthalate composition has a flexural modulus of 2000-25 OOMPa measured according to ISO 178:2001, and a tensile modulus of 2000-2600MPa, and an elongation at break % of 4-15%, measured respectively according to IS0527-2: 1993.

In another embodiment of the monofilament bristle, based on the total weight of the modified polytrimethylene terephthalate composition, at least a polytrimethylene terephthalate and at least a polyethylene-alkyl acrylate copolymer are present in an amount of preferably 86-92 wt.% and 8-14 wt.%) respectively, or more preferably 87-89 wt.% and 1 1-13 wt.% respectively.

In another embodiment of the monofilament bristle, at least a polyethylene-alkyl acrylate copolymer comprised in the modified polytrimethylene terephthalate composition is selected from one or more of the polyethylene- alkyl (Ci-Cio) acrylate copolymers; or preferably selected from polyethylene-methyl acrylate compolyer, polyethylene-ethyl acrylate compolyer, polyethylene- propyl acrylate compolyer, polyethylene-butyl acrylate compolyer, or the combinations of two or more thereof.

In another embodiment of the monofilament bristle, the at least a polytrimethylene terephthalate in the modified polytrimethylene terephthalate has an intrinsic viscosity of 0.8-1.7dl/g, or preferably 0.9-1.4dl/g.

In another aspect of the present invention, a brush comprising the above monofilament bristle is provided. The selected brush could be a toothbrush, a paint brush, a cosmetic brush or an industrial brush. A preferred embodiment of the present invention is a toothbrush.

The polytrimethylene terephthalate used in the present invention can be polyester obtained by the condensation of 1 ,3-propylene glycol and terephthalic acid (or terephthalate). The 1 ,3-propylene glycol used in the preparation of polytrimethylene terephthalate can be obtained preferably via biochemical process from renewable resources (the 1 ,3-propylene obtained via biochemical process).

A person skilled in the art could choose a polytrimethylene terephthalate having single intrinsic viscosity, or concurrently use several polytrimethylene terephthalates with different intrinsic viscosity. Preferably, at least a polytrimethylene terephthalate used in the present invention has an intrinsic viscosity of about 0.8-1.7 dl/g, preferably about 0.9-1.4 dl/g.

A preferred polytrimethylene terephthalate is the polytrimethylene terephthalate produced by E.I.

DuPont de Nemours and Company, USA and marketed as Sorona® (hereinafter referred to as DuPont) and having an intrinsic viscosity of 0.96 dl/g. The starting material 1 ,3-propylene used for making Sorona® polytrimethylene terephthalate is obtained via fermentation of corn sugar.

Therefore, 37% of the starting materials for the polymer may come from natural renewable resources rather than traditional petrochemical feedstock, thereby reducing dependence on mineral and fossil resources. The polyethylene-alkyl acrylate copolymers used in the present invention refer to such copolymer obtained from the copolymerization of ethylene with alkyl acrylate, wherein the main chain comprises a repeating unit derived from the polymerization of ethylene monomers and a repeating unit derived from the polymerization of alkyl acrylate monomer. The alkyl group in the alkyl acrylate could be a straight chain or a branched chain C _1-10 alkyl group, preferably a straight chain or a branched chain Ci_ ₄ alkyl group, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso- butyl or tert-butly. In an embodiment, the polyethylene-alkyl acrylate copolymer used is selected from polyethylene-methyl acrylate copolymer, polyethylene-ethyl acrylate copolymer, polyethylene- butyl acrylate copolymer and the optional combinations thereof. In another embodiment, the polyethylene-alkyl acrylate copolymer used is selected from polyethylene-methyl acrylate copolymer.

In the present invention, based on the total weight of the polyethylene-alkyl acrylate copolymer, the alkyl acrylate monomer unit is present in an amount of preferably about 4-40 wt.%, more preferably of about 8-35 wt.%, most preferably of about 18-30 wt.%.

The polyethylene-alkyl acrylate copolymer used in the present invention can be selected from commercially available polyethylene copolymer, produced by DuPont, USA and marketed as Elvaloyl®AC, or polyethylene-methyl acrylate resin, produced by ExxonMobil Chemical Company and marketed as Optema™.

The methods of preparing polyethylene-alkyl acrylate copolymer are publicly known in the art. For example, see Modern Plastics Encyclopedia and the Wiley Encyclopedia of Packaging

Technology.

In the present invention, based on the total weight of the modified polytrimethylene terephthalate composition, the polytrimethylene terephthalate is present in an amount of about 85-95 wt.%, preferably about 86-92 wt.%, more preferably of about 87-89 wt.%. The polyethylene-alkyl acrylate copolymer is present in an amount of about 5-15 wt.%, preferably of about 8-14 wt.%, more preferably of about 1 1-13 wt.% based on the total weight of the modified polytrimethylene terephthalate composition.

In the present invention, the modified polytrimethylene terephthalate has a flexural modulus of about 2000-2500 MPa measured according to ISO 178:2001 ; and a tensile modulus of about 2000- 2600 MPa, and an elongation at break % of about 4-15% or lower, measured respectively according to IS0527-2:1993.

In order to lower the flexural modulus and tensile modulus of a material, one would likely add soft. Consequently, it could usually be predicted that the elongation at break % would increase accordingly, as soft materials are added to the lower flexural modulus and the tensile modulus. However, the inventors of this invention have surprisingly discovered that the modified

polytrimethylene terephthalate of this invention has a flexural modulus of about 2500MPa or lower, a tensile modulus of about 2600 MPa or lower, and the elongation at break % remains at about 20% or lower. That is, relative to the polytrimethene terephthalate alone, after adding copolymer of polyethylene-alkyl acrylate, the flexural modulus and tensile modulus decrease, but the elongation at break % remain basically the same or even decrease.

On the other hand, during the process of adding soft materials into polyester material, the problem of incompatibility between two materials usually occurs. When two materials have poor compatibility, they may exist respectively in two phases, which could worsen the processability of the material, which in turn will decrease the formability and durability of the product, or directly affect the further extrusion spinning. It has been found, surprisingly, that the polytrimethylene terephthalate and polyethylene-alkyl acrylate copolymer in the modified polytrimethylene terephthalate composition of the invented monofilament bristle can form a homogeneous single- phase or a single phase, and when extruded from the extruder, the formation processability is excellent. This single phase composition also possesses advantages such as being hard to crack and maintaining sufficient stability, even after prolonged use, and thermal deformation and hygroscopic expansion. Therefore, the durability of the finished product, such as a toothbrush, a paint brush, a cosmetic brush, etc., increases.

In the present invention, the term "single-phase" or "single phase" refers to two substances integrating to each other without obvious phase interface between the two under a microscope, or after the materials are mechanically extruded, the section and appearance of the material are homogeneous, without any obvious delamination and phase interface, and unable to be separated by ordinary techniques such as by means of mechanical separation. Optionally, the composition of the present invention may comprise a small amount of existing additives commonly used and well-known in the polymer field. The examples of the additives include without limitation antioxidant, heat stabilizer, UV stabilizer, colorant including dye and pigment, lubricant, anti-hydrolysis agent and flame retardant. These additives in the composition are present in an amount of usually about 0.01-15 wt.%, preferably of about 0.01-10 wt.%, as long as they do not reduce or damage the basic and novel characteristics of the compositions, and do not affect the properties of the composition adversely.

There is no specific restriction on the preparation process of the monofilament bristle in the present invention. It could be any publicly known polymer blending method in the art, including solution extrusion spinning process and melt extrusion spinning process, but preferably melt extrusion spinning process. For example, the monofilament bristle in the present invention can be prepared through the following process: after polytrimethene terephthalate, polyethylene-alkyl acrylate copolymer, and other optionally existing additives are melt-extruded by the extruder, monofilament bristles can be obtained via stretching and shaping, wherein the extruding temperature may be set at about 235-290°C, preferably at about 245-265°C, extruding speed can be at about 200- 400rpm, and throughput can be at about 15-30kg/hr.

The monofilament bristle in the present invention may be used in various areas according to different usages. In a preferred embodiment, the monofilament bristle refers to monofilament bristles used in toothbrushes, paint brushes, cosmetic brushes or industrial brushes.

The invention also provides a brush comprising the monofilament bristles of the present invention. Preferably, the brush of the present invention is a toothbrush, a paint brush or a cosmetic brush. If necessary, toothbrushes, paint brushes, cosmetic brushes or industrial brushes may comprise at least one bunch of the invented monofilament bristles, wherein one bunch of

monofilament bristles comprise at least a monofilament bristle of the present invention, more preferably comprising several bunches of the monofilament bristle of the present invention.

For toothbrushes, paint brushes, or cosmetic brushes, the monofilament bristles of the present invention can be used alone or used in combination with other monofilament bristles comprising other components or fiber, wherein the other components are materials such as polyamide, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), etc. In another preferred embodiment, the brush of the present invention is a toothbrush comprising at least one bunch of monofilament bristles of the present invention, preferably comprising several bunches of the monofilament bristles of the present invention. More preferably, the monofilament bristles used in the toothbrush consist essentially of or consist entirely of the monofilament bristles of the present invention.

Examples:

The invention is further illustrated with the following Examples; but the scope of the invention is not limited by the particular examples contained herein. Unless otherwise stated, all ratios and percents in this application are based on weight.

The materials used in the Examples are:

PTT: a polytrimethylene terephthalate resin, produced by DuPont USA and marketed as

Sorona® polytrimethylene terephthalate resin, having an intrinsic viscosity of 0.96 dl/g;

EMA: a polyethylene -methyl acrylate copolymer resin (comprising 24 wt.% of methyl acrylate), produced by DuPont, USA and marketed as Elvaloyl ^® AC 12024.

Comparative Examples 1-2 and Examples 1-5

In each of the Comparative Examples 1-2 and Examples 1-5, an appropriate amount of PTT and EMA (the weight ratios of each component are listed in Table 1) were dried, pre-blended and melt- blended through a ZSK26 twin-screw extruder (purchased from German company Coperion WP) with the temperature set at 230-255°C, extruding speed set at 350rpm and throughput set at 25kg/hr, to obtain desired compositions.

The trimethylene terephthalate compositions used for Comparative Examples 1-2 and Examples 1-5 were injected into dumbbell-shaped test specimens. The dumbbell-shaped test specimens were molded. The flexural modulus were measured according to ISO 178:2001; the tensile strengths, tensile modulus and elongation at break % were measured respectively according to IS0527-2: 1993.

Test results are listed in Table 1. Table 1

Note 1 : This change rate is the change in percent of flexural modulus or tensile modulus relative to Comparative

Example 1;

Note 2: n/a means not applicable.

Table 1 shows that when the content of EMA in the composition used in Examples 1-5 is increased, the flexural modulus and tensile modulus are decreased. Surprisingly, the elongation at break % didn't increase correspondingly but remained basically the same (Examples 2 and 4) or slightly increased (Example 1), or even decreased (Example 3 and 5).

The above detailed examples are given for the purpose of demonstrating the invention. It should not be understood as limiting the scope of the invention in any way.